Sahih Muslim Book 025, Hadith Number 5345.

Chapter : The Excellence of Tahnik of the new-born child at the time of its birth and of carrying it to a pious person so that he may soften some dates and rub its palate with them, and permissibility of giving name on the day of its birth and the excellence of such names as 'Abdullah, Ibrahim and the names of all the apostles of Allah (may peace be upon him).

Asma' reported that she had become pregnant at Mecca with Abdullah b. Zubair (in her womb) and she (further) said: I set out (for migration to Medina) as I was in the advanced stage of pregnancy. I came to Medina and got down at the place known as Quba' and gave birth to a child there. Then I came to Allah's Messenger (may peace he upon him). He placed him (the child) in his lap and then commanded for the dates to be brought. He chewed them and then put the saliva in his mouth. The first thing which went into his stomach was the saliva of Allah's Messenger (may peace be upon him). He then rubbed his palate with dates and then invoked blessings for him and blessed him. He was the first child who was born in Islam (after Migration).