Hisham bin Urwah narrated from his father and from Fatimah bint al-Mundhir: When Asma' bint Abi Bakr set out to emigrate, she was pregnant with Abdullah bin al-Zubayr. She reached Quba', and her labour began at Quba'. Then, after she had given birth to Abdullah, she set out with him to the Messenger of Allah (peace and blessings be upon him) so that he (peace and blessings be upon him) might perform tahnik for him. The messenger of allah (peace and blessings be upon him) took him from her and placed him in his lap, then called for a date. Aishah (may Allah be pleased with her) said: We searched for it for a while before we found it. Then he (peace and blessings be upon him) chewed it and placed it in his mouth, so the very first thing that entered his stomach was the saliva of the Messenger of Allah (peace and blessings be upon him). Asma' (may Allah be pleased with her) said: Then he (peace and blessings be upon him) wiped him with his hand, supplicated for him and named him Abdullah. Later, when he was seven or eight years old, he came to pledge allegiance to the Messenger of Allah (peace and blessings be upon him); al-Zubayr had instructed him to do so. He (peace and blessings be upon him) smiled when he saw him coming towards him, and then accepted his pledge.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13819