What is the ruling on placing a thermometer wetted with a sterilizing solution or a tongue depressor inside the mouth of a fasting person for medical investigations? Likewise, for the case of entering a finger moistened with water in the mouth for the need of ejecting a foreign body or remnants of food from the mouth while fasting? Should it be dried before entering the mouth?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

Fasting is not invalidated by the mere entry of objects into the mouth even if there is no necessity. It is invalidated by what reaches the stomach. Therefore, the mentioned objects do not invalidate fasting as long as nothing thereof reaches the stomach. It is not necessary to dry the finger before entering it to remove something. Rather, one should be careful that the moistness of water does not reach the throat and then the stomach. It is known that a fasting person may rinse his mouth but he should not be extravagant so as to avoid having any water reach his stomach.

Allaah Knows best.