Sayyidina Ibn Abbas (RA) reported that a villager came to the Prophet (SAW) and confirmed that he had seen the new moon. So, he asked him, “Do you bear witness that there is no God but Allah? Do you bear witness that Muhammad is Allah’s Messenger?” He said, “Yes!” The Prophet said, “0 Bilal! Proclaim to the men that they should fast tomorrow”.
[Abu Dawud 2340, Nisai 2112, Ibn e Majah 1652]
--------------------------------------------------------------------------------