Al-Matalib al-'Aliyah 118 — Things that nullify wudu

It is narrated from Sayyidah Aishah (may Allah be pleased with her) that she said (expressing amazement and as a warning): "One of you performs ablution after eating food (out of concern for outward cleanliness or ablution), yet does not perform ablution (that is, repentance and purification) for the indecent, vulgar and obscene word that he utters with his tongue?"
Imam Musaddad bin Musarhad recorded this narration in his Musnad; all the narrators of its chain are thiqat (trustworthy), and this statement indicates the importance of purifying oneself from the slips of the tongue.