Sunan Abi Dawud 2333
سنن أبي داود#2333SahihAl-Hasan said about a person who was in a certain city. He fasted on Monday, and twp persons bore witness that they had sighted the moon on the night of sunday. He said:That man and the people of his city should not fast as an atonement except that they know (for certain) that the people of a certain city of Muslims had fasted on Sunday. In that case they should keep fast as an atonement
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih Maqtu
Muhammad Muhyi Al-Din Abdul HamidSahih Maqtu
Shuaib Al ArnautMaqtu
Zubair Ali ZaiIsnaad Sahih
In-book reference: 14:21