What is the ruling on swearing falsely by saying: "By my fasting and prayer in this blessed month," while being occupied with something other than that which was sworn upon, and is an expiation (kaffarah) binding upon me, and what is it?

You must repent to Allah for what you have done, as it involved two prohibited acts: swearing by other than Allah, such as swearing by prayer or fasting, which is polytheism (shirk); based on the Prophet’s (peace be upon him) saying: "Whoever swears by other than Allah has committed shirk." And his saying: "Whoever is to swear, let him swear by Allah or remain silent." The second is lying. As for expiation (kaffarah), it is not obligatory, because swearing by other than Allah is prohibited and does not require expiation, but rather repentance. Also, because the oath sworn was not a binding oath concerning a possible future matter, but rather it was based on a lie.