Sahih Muslim Book 025, Hadith Number 5344.

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).

'Urwa b. Zubair and Fatima daughter of Mandhir b. Zubair, reported that Asma' daughter of Abu Bakr was at the time of migration in the family way with 'Abdullah b. Zubair (in her womb). She came to Quba' and gave birth to 'Abdullah at that place and then sent him to Allah's Messenger (may peace be upon him) so that he should rub his palate with chewed dates. Allah's Messenger (may peace he upon him) took hold of him (the child) and he placed him in his lap and then called for dates. 'Aisha said: Some time was spent before we were able to find them. He (the Holy Prophet) chewed them and then put his saliva in his mouth. The first thing that entered his stomach, was the saliva of Allah's Messenger (may peace be upon him). Asma' said: He then rubbed him and blessed him and gave him the name of Abdullah. He ('Abdullah) went to him (the Holy Prophet) when he had attained the age of seven or eight years in order to pledge allegiance to Allah's Messenger (may peace be upon him) as Zubair had commanded him to do. Allah's Messenger (may peace be upon him) smiled when he saw him coming towards him and then accepted his allegiance.