Silsilat al-Ahadith al-Sahihah

Sayyiduna Abdullah bin Abbas (may Allah be pleased with them) narrates that the Noble Prophet (peace and blessings be upon him) said: "Satan comes to a person and blows at his backside (i.e., the place of excretion) to cast doubt (in him). (In such a case) a person should not go (to perform ablution) until he hears a sound or perceives a smell."