Some hold that these are its initial Source.
When the desire arose in the mind of Muhammad to draw his people from the
worship of idols to that of God Almighty; and when he remembered that their
forefathers in the days of Abraham believed in the divine Unity; and further
that they inherited many of the beliefs and customs of their pious
forefathers; he was unwilling to force abandonment of them all, but desired
rather to purify their faith, and to maintain such ancient practices as he
thought good and reasonable. And so we find this passage in the Qur'an: Who
is better than he that resigneth himself to God, and worketh righteousness,
and followeth the religion of Abraham the faithful? and truly God took
Abraham for his friend (Surah iv. 124). And again: Say, The Lord
speaketh truth; follow ye, therefore, the faith of-Abraham the righteous;
for he was no idolator (Surah iii. 89). And yet once more: Say,
Verily my Lord hath directed me into the right way, the true faith, the
religion of righteous Abraham, and he was no idolater (Surah vi. 89).