Musnad Ahmad 1167:27

Abu Usamah narrated to us, from Hisham, from his father, from Asma, that she was pregnant with Abdullah ibn al-Zubayr in Makkah. She said: "I went out while I was at full term, and I arrived in Madinah, and I stayed at Quba, and I gave birth to him at Quba. Then I brought him to the Prophet, peace and blessings of Allah be upon him, and he placed him in his lap. Then he called for a date, chewed it, and spat it into his mouth, so the first thing that entered his stomach was the saliva of the Messenger of Allah, peace and blessings of Allah be upon him." She said: "Then he performed tahnik on him with a date, then he prayed for him and invoked blessings upon him. And he was the first newborn born in Islam."