Musannaf Ibn Abi Shayba 36:88

Khalid ibn Makhlad narrated to us, from Ali ibn Mushir, from Hisham ibn Urwah, from his father, from Asma bint Abi Bakr, that she migrated to the Messenger of Allah (may Allah bless him and grant him peace) while she was pregnant with Abdullah ibn al-Zubayr. She gave birth to him at Quba, and she did not breastfeed him until she brought him to the Prophet (may Allah bless him and grant him peace). He took him and placed him in his lap. They searched for a date to perform the *tahnik* (softening it and rubbing it on the palate) for him until they found one. They performed the *tahnik* for him, so the first thing that entered his stomach was the saliva of the Messenger of Allah (may Allah bless him and grant him peace), and he named him Abdullah.