From Sahih Bukhari (Hadith 5469):
Narrated Asma' bint Abu Bakr:I conceived `Abdullah bin Az-Zubair 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: Bukhari 5469