What is the ruling on washing or rinsing the mouth for ablution (wudhu) or when brushing one’s teeth during fasting?
Rinsing the mouth is recommended for ablution (wudhu), yet the fasting person should ensure that they do not swallow any water. If that water inadvertently enters the esophagus, the fast remains valid. However, if rinsing the mouth was not for ablution (wudhu), then the fast would be invalid [if water entered the esophagus]. It is permissible for a fasting person to use a toothbrush to clean their teeth during the day provided they do not swallow anything. A very minute amount that usually dissolves in the saliva does not break the fast, and the fasting person should spit out all the water they rinsed with after brushing their teeth (e.g., by spitting three times) to ensure that nothing goes down the esophagus.