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."
Reference: Sunan an-Nasa'i 2126 In-book : Book 22, Hadith 37 English translation : Vol. 3, Book 22, Hadith 2128
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