Musannaf Ibn Abi Shaybah

Once, Hazrat Umar saw a man scratching his armpit. He said to him, "Get up and wash your hand or perform ablution."

Hazrat Umar says: Whoever cleans his nose or scratches his armpit should perform ablution.

Hazrat Ibn Abbas (may Allah be pleased with them) says that removing the hair of the armpit does not break wudu.

Hasan was asked about the person who touches the armpit or plucks the hair, so he replied: There is no harm in it, but if blood comes out, then the ablution will be broken.

Muhammad says that people say that one who touches the armpit should perform ablution again; I neither say this nor do I know of this matter.

Hazrat Abdullah bin Amr (may Allah be pleased with him) used to perform ghusl after plucking the hair of a mule.