On the authority of Talhah Ibn Ubayd Allah (may Allah be pleased with him) who reported that the Prophet (PBUH) would say when he saw the crescent moon: "O Allah, let this moon appear over us with blessings and faith, safety and Islam. My Lord and your Lord is Allah."

This was narrated by Tirmidhi (Hadith no. 3451), who said: "It is a Hasan (good) Hadith."

And Allah The Almighty Knows Best.