´It was narrated from Ribii bin Hirash, from Hudhaifah bin Al-Yaman, that the Messenger of Allah said:` "Do not anticipate the month until you see the crescent before it, or you complete the number of days. Then fast until you see the new moon, or you complete the number of days."
Hadith Referenceسنن نسائي / كتاب الصيام / 2128
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:إسناده صحيح