Abraham was 86 according to the biblical account Gen16:16, when Hagar gave birth to Ishmael. The root of the name in both Hebrew/ishma and Arabic/ismaa implies "hearing". This is because in both the Bible and the Quran, Abraham desperately prays God for a son. In the Bible God "hears" both his and Hagar's prayers Gen15,16 while the Quran cites only Ibrahim's prayers for a righteous son 37:100-1 and which Allah heard/ismaa. He thus named that firstborn son he longed for Ismaail/Ishmael (a similar Biblical case is Samuel whom his mother called so because 1Sam1:20"I asked him of the Lord").
Ismail was the manifestation of Allah's acceptance of Ibrahim's prayers
14:39"Praise be to Allah, Who has given me in old age Ismail and Ishaq; most surely my Lord is the Hearer of prayer".
It is to be noted that both Ishmael and Ismail are appropriation into Hebrew/Arabic of the name which Abraham gave to his son in his native Babylonian language. Ismail's birth was a miracle given Ibrahim's old age, and God, throughout the prophetic history caused women to bear children in miraculous circumstances, Mary the mother of Jesus being one of them
19:20,3:47"Allah creates what He pleases; when He has decreed a matter, He only says to it, Be, and it is".
The Abrahamic connection with the Arabs, Mecca, the Kaaba was deeply ingrained in the minds of the prophet's addressees. There was no tension nor polemics in that regards, neither with the polytheists, nor with the Jews and Christians among the Arabs. This bellies the notion that, whomever the critics alledge wrote the Quran, needed to invent that connection.
Recently for instance Joseph Witztum argued the Quranic Ishmael-binding narrative and building of the Kaaba by both Ibrahim and his son, find inspiration in a Syriac Homily by Jacob of Serugh. Besides Witztum's admission that the Abrahamic connection with the Meccan Ishmaelites is attested in non Muslim pre-Islamic sources (Theodoret and Sozomon), meaning the Quran did not need re-adapting a story to make a point that was already accepted, no evidence exists for the Homily in question circulating among the Arabs of the peninsula, including Jews and Christians. Especially not among the laymen, making the information complicated to access, even more so in the Arabic language. No loan words or linguistic similarities appear in the parallel passages. The similarities are isolated and out of context. For example the homily speaks of Abraham and Isaac building an altar. Although there is mention of both Ibrahim and Ismail engaging in construction, there is no altar or sacrifice in the Quranic context. Neither were the Kaaba nor the altar to sacrifice the enigmatic "only son", which could never have been Isaac the second-born, the only spiritual constructions by Abraham. The Bible recounts how he built places of worship to God throughout his journeys Gen12:6-8,13:4,18. That Abrahamic practice we are told in the HB, was left to his posterity that similarly built places of worship symbolized by stones erected as pillars Gen28:10,18-22, ie the "foundations" which Ibrahim and Ismail "raised" 2:127.
On a more general note, the idea the Arabs needed to express their thoughts, even their sacred history in a foreign language, such as Syriac is untenable. Christoph Luxenberg famously stated that the Syro-Aramaic used in Edessa and its environs is the original language of the Quran, not Arabic, despite the Quran itself repeatedly saying about itself it is evident Arabic, in the language of the messenger's people 12:2,13:37,26:195,46:12,16:103,19:97,44:58,14:4. One may add that the consensus of all Arabs after Islam, regardless of their scholarly, political and tribal background is that the Quran has been revealed in the Qurayshi dialect, whose language was known for its eloquence. Neither does Luxenberg explain how this language might have come to dominate in far away Hijaz to such an extent that it would form the basis of the sacred writings of its inhabitants, nor does he present the slightest evidence that there existed in Mecca and its surroundings an Arab community under intense Christian influence. These claims run along the same lines as those of the Protestant theologian Gunter Luling who theorized in the 1960s that this area was thoroughly christianized by Muhammad’s lifetime, and Mecca was a significant Christian town ruled by the Quraysh, a Christianized tribe that worshipped in the Kaaba, a Christian church built with an orientation toward Jerusalem. This assertion however remains unsubstantiated whether from Muslim or Christian sources, just as his assumption of a massive Christian presence in central and northwestern Arabia.
There are no Arabic inscriptions written in the Syriac script whereas there are quite a number of them written in Nabataean Aramaic script, the recognized origin of the Arabic script. Arabic was widely spoken in the Middle East by the 7th century CE, particularly in the region of the former Nabataean kingdom. This very evolution presumes frequent writing of Arabic in the Nabataean script. Some inscriptions prove that Arabic had already long been used for sacred expression, such as the Oboda inscription, and possibly also the ones found in the Madaba area. There is also Epiphanius of Salamis’ testimony as to the praises to a virgin deity sung in Arabic by the inhabitants of Petra and Elusa.
A well known Meccan inscription dated to AH 98/717 CE is variously attributed to a bishop of Najran in southwest Arabia named Quss ibn Sa‘ida, or else to one of the pre-Islamic kings of Yemen. Regardless of the authenticity of that attribution, the accumulation of pre-islamic evidence, including a vast wealth of poetry, does point to them belonging to that period. The pre-Islamic Arabic texts are nothing but the visible tip of the iceberg. Most of the hidden material is lost through the effect of time or in the process of being discovered. The point is that there is a substantial tradition of writing and speaking Arabic. Why would then the Quran's supposed authors need to express their sacred traditions in a far away foreign language?
Further reading answering The Islam Issue "Gods house of plagiarism"
The Qibla change
Abraham and the Kaaba
The only son
The seven sleepers
