Pope Shenouda III
The sinful fasts during the days of the Prophet Jeremiah:
The Lord did not accept this fast and said to Jeremiah, “Do not pray for this people, for their good. "When they fast, I will not hear their cry; and when they offer burnt offering and grain offering, I will not accept them. But I will consume them.” (Jer 14:11,12).
The Lord did not accept their fasts, prayers, and oblation because they lived an evil life and their hearts were not pure before Him.