Asma bint Abu Bakr reported,

I set out while I was in the final stage of pregnancy and arrived at Medina, where I stopped at Quba and gave birth to him there. Then I brought him to the Messenger of Allah ﷺ, who placed him in his lap. He called for a date, chewed it, and then placed his saliva into the child's mouth. The first thing to enter the child's stomach was the saliva of the Messenger of Allah ﷺ. Then he rubbed the chewed date on the child's palate, prayed for him, and invoked blessings upon him. He was the first child born in Islam.

Muslim 5617

Sahih

حدثنا أبو كريب محمد بن العلاء حدثنا أبو أسامة عن هشام عن أبيه

عن أسماء أنها حملت بعبد الله بن الزبير بمكة قالت

فخرجت وأنا متم فأتيت المدينة فنزلت بقباء فولدته بقباء ثم أتيت رسول الله ﷺ فوضعه في حجره ثم دعا بتمرة فمضغها ثم تفل في فيه فكان أول شيء دخل جوفه ريق رسول الله ﷺ ثم حنكه بالتمرة ثم دعا له وبرك عليه وكان أول مولود ولد في الإسلام

مسلم 5617صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Muslim
Book
Etiquette
Chapter
Recommendation of chewing a date and rubbing it on the palate of a newborn at birth, carrying him to a righteous person to do so, permissibility of naming him on the day of his birth, and recommendation of naming with Abdullah, Ibrahim, and other names of the prophets, peace be upon them
Numbering
Darussalam 5617
Muslim 5617