(1) باب تَسْمِيَةِ الْمَوْلُودِ غَدَاةَ يُولَدُ، لِمَنْ لَمْ يَعُقَّ عَنْهُ، وَتَحْنِيكِهِ
Narrated Asma' bint Abu Bakr:
I conceived `Abdullah bin AzZubair at Mecca and went out (of Mecca) while I was about to give birth. I came to Medina and encamped at Quba', and gave birth at Quba'. Then I brought the child to Allah's Messenger (ﷺ) and placed it (on his lap). He asked for a date, chewed it, and put his saliva in the mouth of the child. So the first thing to enter its stomach was the saliva of Allah's Messenger (ﷺ). Then he did its Tahnik with a date, and invoked Allah to bless him. It was the first child born in the Islamic era, therefore they (Muslims) were very happy with its birth, for it had been said to them that the Jews had bewitched them, and so they would not produce any offspring.
Reference: Sahih al-Bukhari 5469
In-book reference: Book 71, Hadith 3
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 7, Book 66, Hadith 378