Musnad Abu Ya'la al-Mawsili 6:129

Ahmad ibn Ibrahim narrated to us, also Abu Dawud narrated to us, Shu'bah narrated to us, from Qatadah, who said: I heard Yunus ibn Jubayr narrating from Muhammad ibn Sa'd ibn Abi Waqqas, from Sa'd, that the Messenger of Allah (may Allah bless him and grant him peace) said: "For the interior of one of you to be filled with pus is better for him than for it to be filled with poetry."