Hazrat Ibn Abbas (may Allah be pleased with both of them) and Hazrat Sha'bi say that if one was performing ablution (wudu) for any purpose other than prayer, then he must make up (qada) for that fast. If he was performing ablution for prayer, then making up is not obligatory upon him.

9736 - From Hurayth, from al-Sha‘bi, they said: If it was for other than prayer, he must make it up, and if it was for prayer, there is no making up upon him.

Hasan used to say that if someone rinses their mouth while fasting and water unintentionally goes down their throat, then nothing is required of him. He will complete his fast.

Hazrat Hammad says that if, while rinsing the mouth, water enters the throat of a fasting person, then if ablution was obligatory, nothing is required of him. If he was rinsing the mouth for any other reason, he must repeat the fast.

Hazrat Ibn Jurayj says that a man asked Hazrat Ata that while I was cleaning my nose, water went down my throat; is there any harm in this? He replied, there is no harm in this, you do not have control over it.

Ibrahim, regarding the fasting person into whose throat water from ablution enters, states that if he remembers his fast, he will make it up, and if he does not remember his fast, then nothing is required of him.

Hazrat Amr bin Harm narrates that Hazrat Jabir bin Zaid was asked: If a person is fasting and while performing ablution, water enters his throat, will his fast be broken? He replied: No, he should complete his fast.