People of the Book—the Jews, the Christians and the Muslims have common terms, primarily belief in none but God, and the belief translates into worship of God, as laid down:
'Say, O People of the Book, come to terms common between us and you: that we worship none but God, and we associate nothing with Him, and none of us takes others as lords besides God. And if they turn away, say, Bear witness we have submitted' (3:64)
The word is clear that common terms between Ahl-ul-Kit'ab is worship of none but God, with a clear interjection that none may be associated with Him, and there are no lords beside God. In case, they don't register the word, then it is to be conveyed in clear terms that they should Bear witness that we have submitted, and one who submits is a Muslim.
Having cleared the common denominator of Ahl-ul-Kit'ab, in the Holy Verse following the one quoted above, it is implied that there should be no room for argument regarding Abraham/ Syedena Ibrahim (AS):
''O People of the Book! Why do you argue about Abraham, when the Torah and the Gospel were not revealed until after him? Will you nor reason?'' (3:65)
Torah and Bible were not revealed until after Abraham/ Syedena Ibrahim (AS) so there should be no room for an argument, as he could hardly be expected to follow scriptures which were revealed after him.
It is clearly implied that argument, if any may be restricted to things within knowledge, not about things beyond the realm of knowledge, known only to God:
''Here you are, you argue about things you know, but why do you argue about things you do not know? God knows and you do not know'' (3:66)
Finally the faith of Abraham/ Syedena Ibrahim (AS) is clearly revealed:
'Abraham was neither a Jew nor a Christian, but he was a Monotheist, a Muslim. And he was not of the Polytheists' (3:67)