«كان إذا رأى الهلال قال: اللهم أهله علينا باليمن والإيمان والسلامة والإسلام ربي وربك الله»
It was the practice of the Prophet (peace and blessings be upon him):
"When he (peace and blessings be upon him) saw the new crescent moon, he would say: O Allah, let it rise over us with blessing and faith, with safety and Islam. O moon, my Lord and your Lord is Allah."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4726