Musnad Ahmad 730
It was narrated that Ibn al Hanafiyyah said:
`Ali (رضي الله عنه) said: O Messenger of Allah (ﷺ), if I have a son after you are gone, I will call him by your name and give him your kunyah. He said: `Yes.` That was a concession from the Messenger of Allah (ﷺ)  to `Ali.
حَدَّثَنَا وَكِيعٌ، حَدَّثَنَا فِطْرٌ، عَنِ الْمُنْذِرِ، عَنِ ابْنِ الْحَنَفِيَّةِ، قَالَ قَالَ عَلِيٌّ رَضِيَ اللَّهُ عَنْهُ يَا رَسُولَ اللَّهِ أَرَأَيْتَ إِنْ وُلِدَ لِي بَعْدَكَ وَلَدٌ أُسَمِّيهِ بِاسْمِكَ وَأُكَنِّيهِ بِكُنْيَتِكَ قَالَ نَعَمْ فَكَانَتْ رُخْصَةً مِنْ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ لِعَلِيٍّ‏.‏