Sunan an-Nasa'i 2126
سنن النسائي#2126SahihIt 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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiIsnaad Sahih
In-book reference: 22:37