Authentic Supplication Number 216.
It is reported by way of ‘`Abdillah bin `Amr that a man asked the Prophet : Which of Islam is the best? He said: “To feed the food and to recite As-Salam upon whom you know and whom you don’t know.”
Agreed upon by Bukhari and Muslim. Al-Albani included this hadeeth in The Authentic of Good Sayings as #153.