Certainly, Abdullah bin Abd al-Muttalib is the actual father of the Prophet ﷺ and this was well known to Quraysh. The evidence is from Sahih Al-Bukhari:
- When Suhail bin Amr came to write the treaty of peace in Al-Hudaybiyah, he said, "Write a book between us and you" . So, the Prophet (ﷺ) called the clerk and said to him, "Write: By the Name of Allah, the most Beneficent, the most Merciful." Suhail objected and said, "As for 'Beneficent,' by Allah, I do not know what it means. So write: By Your Name O Allah", The Prophet (ﷺ) said, "Write: By Your Name O Allah". Then He dictated, "This is the peace treaty which Muhammad, Allah's Messenger has concluded." Suhail objected and said, "By Allah, if we knew that you are Allah's Messenger we would not prevent you from visiting the Ka`ba, and would not fight you. So, write: "Muhammad bin `Abdullah." The Prophet (ﷺ) said, "By Allah! I am Apostle of Allah even if you people do not believe me. Write: Muhammad bin `Abdullah".
This proves that the lineage of the Prophet was well known, and that He was the son of Abdullah, and Quraysh had no doubt about that.
- In the dialogue that took place between Hercules and Abu Sufyan, the first question Hercules asked about the lineage of the Prophet, and Abu Sufyan's answer was "He is of noble lineage", and Abu Sufyan was not a Muslim at the time, and if there had been any doubt about the Prophet's lineage, Abu Sufyan would not have wasted the opportunity to question the truth of the Prophet's lineage, but he did not do so for fear of being accused of lying.