Musnad Abu Ya'la al-Mawsili 116:11

A garment of silk was brought to the Messenger of Allah, may Allah bless him and grant him peace. They began to touch it and marvel at its softness. The Messenger of Allah, may Allah bless him and grant him peace, said: "The handkerchiefs of Sa'd ibn Mu'adh in Paradise are better than this, or softer than this."