Imam Abu Bakr (may Allah have mercy on him) says that in the narration of Hazrat Talhah bin Ubaidullah, regarding the question about Islam from the Prophet Muhammad (peace be upon him), it is mentioned that the Prophet (peace be upon him) said: "And the fasting of Ramadan (is obligatory upon you)." He asked, "Are there any other fasts obligatory upon me besides this?" The Prophet (peace be upon him) said: "No, except that you observe voluntary fasts."