Musnad Ahmad 1018:8

Waki’ narrated to us, Sufyan narrated to us, from Mansur, from Rib’i ibn Hirash, from some of the companions of the Messenger of Allah (may Allah bless him and grant him peace), who said: The people woke up fasting for the completion of thirty [days]. He said: Then two Bedouins came and testified that they had sighted the crescent yesterday. So the Messenger of Allah (may Allah bless him and grant him peace) commanded the people, and they broke their fast.