What is the ruling on cleaning the teeth with a toothbrush and toothpaste for the one who is fasting?
Machine translationRead the Arabic original
The questioner : We would also like to know the ruling on brushing the teeth with a toothbrush and toothpaste after the Fajr adhan or during the adhan?
The Shaykh : During the time before it, regarding eating and drinking. Yes. And it is greater than.
The questioner : The toothbrush, yes.
The Shaykh : As for after the adhan, the most correct view is that it is after the appearance of the dawn. Whether immediately or during the day, there is no harm in a person cleaning his teeth with a toothbrush and toothpaste. However, given the strong penetration of the toothpaste, a person should not use it while fasting, because it goes down to the throat and stomach without the person being aware of it. And there is no dire necessity calling for it, so let him abstain until he breaks his fast, and let him do this at night, not during the day. But in principle, it is permissible and there is no harm in it.
The Shaykh : During the time before it, regarding eating and drinking. Yes. And it is greater than.
The questioner : The toothbrush, yes.
The Shaykh : As for after the adhan, the most correct view is that it is after the appearance of the dawn. Whether immediately or during the day, there is no harm in a person cleaning his teeth with a toothbrush and toothpaste. However, given the strong penetration of the toothpaste, a person should not use it while fasting, because it goes down to the throat and stomach without the person being aware of it. And there is no dire necessity calling for it, so let him abstain until he breaks his fast, and let him do this at night, not during the day. But in principle, it is permissible and there is no harm in it.
Source
ابن العثيمين - فتاوى الصيام — archive.org (10:56)
The Arabic text is a machine transcription of the audio recording.