Asma bint Abu Bakr reported,

I set out while I was in the final stage of pregnancy. I reached Madinah and stopped at Quba, where I gave birth to him. Then I brought him to the Prophet ﷺ and placed him in his lap. He called for a date, chewed it, and then placed it into the child's mouth. So the first thing to enter his stomach was the saliva of the Messenger of Allah ﷺ. Then he rubbed his palate with the date, supplicated for him, and blessed him. He was the first child born in Islam.Khalid bin Makhlad corroborated this, narrating from Ali bin Mushir, from Hisham, from his father, from Asma , that she emigrated to the Prophet ﷺ while she was pregnant.

حدثني زكرياء بن يحيى عن أبي أسامة عن هشام بن عروة عن أبيه

عن أسماء رضي الله عنها أنها حملت بعبد الله بن الزبير قالت

فخرجت وأنا متم فأتيت المدينة فنزلت بقباء فولدته بقباء ثم أتيت به النبي ﷺ فوضعته في حجره ثم دعا بتمرة فمضغها ثم تفل في فيه فكان أول شيء دخل جوفه ريق رسول الله ﷺ ثم حنكه بتمرة ثم دعا له وبرك عليه وكان أول مولود ولد في الإسلام تابعه خالد بن مخلد عن علي بن مسهر عن هشام عن أبيه عن أسماء رضي الله عنها أنها هاجرت إلى النبي ﷺ وهي حبلى