Narrated Aisha:
The first child who was born in the Islamic Land (i.e. Medina) amongst the Emigrants, was ‘Abdullah bin Az-Zubair. They brought him to the Prophet. The Prophet took a date, and after chewing it, put its juice in his mouth. So the first thing that went into the child’s stomach, was the saliva of the Prophet.
Sahih Bukhari, Volume 5, Book58, Number 249