The Islamic name ابرهيم ʔibrāhīm, has always been somewhat puzzling. While this is of course the same name as our Abraham̨ from the Hebrew ʔaḇråhåm, we are left with an unanswered problem in the final syllable, which has randomly shifted the final ā to ī.
Many Arabists invoke 'Imālah' to explain this. Imālah being the shift from ā towards ī. They will then also often state that the name was probably pronounced [ʔibrāhēm]. They take the fact that the name is spelled ابرهيم <ʔbrhym> in most of the Quran but ابرهم <ʔbrhm> in Sūrat al-Baqarah as a 'smoking gun' that the word once had a long /ā/, which got 'Imālized' to /ē/.
The problem with the term 'Imālah' is, is that it is purely descriptive. There is no regular process in Classical Arabic (or the reading traditions) that would cause the /ā/ to shift to /ē/ in this context. In other words: Imālah simply is an Arabic word for saying "The expected /ā/ is now an /ē/". This is not ideal. Several cases of /ē/ in the reading traditions are actually ancient contrasts, as shown by Jabal al-Lughat in this and this post, and developed further in an article of mine published in AEN. Calling these 'Imālah of the ā', is actually anachronistic and the wrong way around. It is rather /ē/ that has shifted to /ā/ in Classical Arabic.
There are other cases of ʔimālah that do look like a shift of ā > ē, for example, in the Warš (and Dūrī, As-Sūsī) tradition, for example stem-final ār followed by the genitive -i shifts to ēri, e.g. an-nāri in Q3:10 is pronounced an-nēri. This is more or less a form of i-umlaut, although it puzzlingly does not apply to ever sequence of āri in the tradition, giving it a veneer of artificiality, but at least a regularly explicable artificiality.
The "ʔimālah" of ʔibrāhām > ʔibrāhēm, however, is not explained by this.
Another puzzling bit of this name in the Quran is the way that it is read in the tradition of Hišām. Here the name is read as ʔibrāhām in some cases, reflecting the ancient pronunciation that we might expect, while in other cases it is read ʔibrāhīm agreeing with all other reading traditions.
As one may expect, all 15 attestations of the name in Sūrat al-Baqarah, where it is always spelled ابرهم <ʔbrhm> in the Cairo edition are indeed read as /ʔibrāhām/. But throughout the rest of Quran, where the Cairo edition consistently has ابرهيم, the name is still read /ʔibrāhām/ a grand total of 18 of the remaining 54 attestations (that's 61% of all attestations!). The distribution of it is pretty unruly, Q60:4 is even read with the first ʔibrāhīm as /ʔibrāhām/ and the second as /ʔibrāhīm/!
Someone used to looking at old Quran documents, might remember that the strict split of ابرهم <ʔbrhm> in Sūrat al-Baqarah and ابرهيم <ʔbrhym> everywhere else is not as strict in older Quran documents, where ابرهم <ʔbrhm> may also appear elsewhere. One might wonder whether there is a correlation between Hišām's reading, and when such spellings show up, and indeed this is the case!
I decided to first check the Samarkand Codex and the Codex Parisino-Petropolitanis (Samarkand and CPP going forward). Here we find that the attestations in Q4 agree with Hišām: Q4:54 has ابرهيم and the three other attestations have ابرهم agreeing perfectly with how it is read in the Hišām tradition.
Likewise Q19 has three attestations, all of which are read as /ʔibrāhām/ and in the Samarkand codex two of those are found, and both are spelled ابرهم <ʔbrhm>.
But there are also disagreements:
Q6:161 /ʔibrāhām/ is spelled ابرهيم <ʔbrhym> in both.
Q9:114 has /ʔibrāhām/ twice, and CPP spelled both of them ابرهيم <ʔbrhym> (unattested in Samarkand)
Q14:35 has /ʔibrāhām/ but CPP spells it ابرهيم <ʔbrhym> (unattested in Samarkand)
Q42:13 has /ʔibrāhām/ but CPP spells it ابرهيم <ʔbrhym> (unattested in Samarkand)
Surprisingly, the Samarkand Codex spelled the last four attestations in Sūrat al-Baqarah as ابرهيم <ʔbrhym>, and therefore disagrees with Hišām reading and the Cairo edition.
What is important to note here is that, whenever these two codices disagree with the Hišām reading, they always disagree in the direction of the spelling ابرهيم <ʔbrhym> which is the 'normal' way of spelling this name. This is probably not a coincidence.
While these similarities are already quite striking and probably significant, the deviations make up a pretty significant percentage of the attested spellings of the name, Samarkand: 5/30 = 16%; CPP: 5/17 = 29%.
I then turned to the probably later, but much more complete Großer Korankodex. There is no clear dating, but people seem to place it paleographically around the start of the 8th century. This Koran codex actually contains all attestations 69 attestations of the name Abraham, although I think we can safely discard the one attestation in Q3:33, which is quite obviously a completely different and much later hand. That still leaves us with 68 attestations. So how does it hold up?
Places where Hišām reads /ʔibrāhām/ where the Großer Korankodex has ابرهم <ʔbrhm>:
Q2:124, 125 (2x), 126, 130, 132, 133, 135, 135, 150, 258 (2x), 260; Q4:125 (2x), 163; Q6:161; Q9:114 (2x); Q14:35; Q16:120, 123; Q19:41, 46; Q29:31; Q42:13; Q51:24; Q53:37; Q57:26; Q60:4 (the first of the two, as in Hišām)
Places where Hišām reads /ʔibrāhīm/ where the Großer Korankodex has ابرهيم <ʔbrhym>:
Q3:65, 67, 68, 84, 96, 97; Q4:54; Q6: 75, 83; Q11:69, 74, 75, 76; Q12: 6, 38; Q15:51; Q21:51, 60, 62, 69; Q22:26, 43, 78; Q26: 69; Q29: 16; Q33: 7; Q37: 83, 104, 109; Q38: 45; Q43: 26; Q60:4 (the second of the two, as in Hišām); Q87: 19.
Then there are a few disagreements:
Places where Hišām reads /ʔibrāhām/ where the Großer Korankodex has ابرهيم <ʔbrhym>:
Q2:127 (it is a little difficult to read, the denticle might be a later addition); Q19:58
(Q2:125 and Q2:132 appear to have a denticle added at a later point, the ductus is clearly very different for Q2:125; not so much for Q2:132, but it looks very different from all other ابرهيم spellings)
Places where Hišām reads /ʔibrāhīm/ where the Großer Korankodex has ابرهم <ʔbrhm>:
In other words, despite a significantly larger amount of attestations, the number of disagreements is still lower than the other two codices, just 5% being wrong (4/68). This is a spectacular correlation, which cannot be attributed to chance. And therefore must mean something, but what?
There are I think two main options:
- The tradition of Hišām is based on a Codex very closely related to this codex.
- This codex is, in fact, attempting to be a transcription of the Hišām reading tradition.
1. If the tradition of Hišām is based on a Codex closely related to this codex, that would have several big implications. It would, first, mean that the tradition is strongly based on a Quranic text, rather than that the text is derived from the tradition.
In several other traditions, this dependency on a Codex is a not obvious. Warš, for example, has /ē/ vowels in etymologically correct places where none of the Codices ever write an <y> that one would expect. Nor do the Codices ever write /ē/ with a ي <y> in words like ʔan-nēri النار, which is never spelled **النير <ʔlnyr>. There is of course no reason to believe that what is true for Warš is necessarily true for Hišām.
If we do accept that the tradition is based on a written examplar, we can argue that the reading /ʔibrāhām/ is completely post-hoc, as a reading /ʔibrāhīm/ from ابرهم <ʔbrhm> would require one to read a long ī while it is not written (which is unique to this word in the Quran ).
2. If the codex is attempting to transcribe the Hišām reading tradition, this would mean that there is something significant about the alternation /ʔibrāhīm/~/ʔibrāhām/. So important, in fact, that scribes found it important enough to encode it into the consonantal skeleton of the text, which is otherwise notoriously bad at expressing the classical Arabic-like reading traditions.
There seems, to me, little reason to assume that this alternation is relevant. There's little doubt that ʔibrāhīm, regardless of spelling, is the same figure. That two competing pronunciations where present, and so relevant that both are used within a single Aya (Q60:4) seems incredibly difficult to motivate.
I therefore prefer the explanation that Hišām is based on a written Codex very close to the Großer Korankodex, and in fact, also clearly related to Samarkand and CPP, but further removed from whatever the Cairo Edition was based on (which is somewhat of a black box).
The tradition of Hišām probably did not come up with ʔibrāhām out of thin air of course. It may show some awareness of the fact that the Jews and Christians called this figure Abraham, and not Abrahim.
This suggests that the ابرهم/ابرهيم <ʔbrhm/ʔbrhym> alternation was much more widespread in older documents, but clearly in a somewhat conventionalized way. Variations that we find in between different manuscripts on these spellings should allow us to reconstruct Stemmata of different manuscript traditions.
This still leaves us with the problem that we do not quite understand why the alternation exists at all. But it does not seem likely that the Hišām tradition is going to give us the answer.
There are two cases in the Cairo edition where /ē/ seems to be transcribed with no sign at all, where it is normally transcribed with ي <y>, namely in Q91:13 سقيها <sqyhʔ> /suqyē-hā/ and 15 عقبها <ʕqbhʔ> /ʕuqbē-hā/, which clearly are placed in a Sūrah with |ēhā|-rhyme. If we take this a possible - but for some reason very rarely used - way of writing word-internal /ē/, then one can carefully suggests that ابرهم/ابرهيم indeed represent /ʔibrāhēm/, but one wonders how a mass amnesia about the pronunciation of the name of a rather central figure (and common Islamic name already in the early Islamic period) would have come about.
 An interesting sidenote is that Hišām is a transmitter of the reader ibn ʕāmir al-Dimašqī, the other transmitter, ibn Ḏakwān, simply always reads ʔibrāhīm as such, independent of the spelling.
 It's a little more complex than that, but all the other cases can be explained through regular orthographic practices, this one cannot.