Sahih al-Bukhari 4782
Sahih al-Bukhari · Book 65: Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh)) · "Call them (adopted sons) by (the names of) their fathers. That is more just with Allah..." (V.33:5)
Narrated `Abdullah bin `Umar:
حَدَّثَنَا مُعَلَّى بْنُ أَسَدٍ ، حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ الْمُخْتَارِ ، حَدَّثَنَا مُوسَى بْنُ عُقْبَةَ ، قَالَ حَدَّثَنِي سَالِمٌ ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ أَنَّ زَيْدَ بْنَ حَارِثَةَ، مَوْلَى رَسُولِ اللَّهِ صلى الله عليه وسلم مَا كُنَّا نَدْعُوهُ إِلاَّ زَيْدَ ابْنَ مُحَمَّدٍ حَتَّى نَزَلَ الْقُرْآنُ {ادْعُوهُمْ لآبَائِهِمْ هُوَ أَقْسَطُ عِنْدَ اللَّهِ} .
We used not to call Zaid bin Haritha the freed slave of Allah's Messenger (ﷺ) except Zaid bin Muhammad till the Qu'anic Verse was revealed: "Call them (adopted sons) by (the names of) their fathers. That is more than just in the Sight of Allah." (33.5)