Sila bin Zufar narrates: We were present with Sayyiduna Ammar bin Yasir (may Allah be pleased with him). A roasted goat was brought before him. He said: Come forward. Then one person withdrew. He explained: I am fasting. So Sayyiduna Ammar bin Yasir (may Allah be pleased with him) said: Whoever fasts on the day about which there is doubt (whether it is a day of Ramadan or not), then that person has disobeyed Sayyiduna Abul Qasim (the Prophet Muhammad, peace be upon him).