What is the ruling on the fast of one who fondled his wife during the daytime in Ramadan after Fajr, and inserted his finger into her vagina without emission from him or her; is his fast valid or invalid?

A fasting person must avoid anything that invalidates the fast. Caressing one's wife poses a significant risk to the validity of the fast. If there is no seminal emission, the man's fast is valid. However, the wife's fast is invalidated, based on the principle that the entry of anything into the vagina invalidates the fast, which is the view of many scholars. The precautionary measure is to make up the fast to avoid scholarly disagreement.