Musnad Ahmad 27:676

Muhammad ibn Ja'far narrated to us, Shu'bah and Hajjaj narrated to us, they said: Shu'bah narrated to me, I heard Qatadah narrating from Bakr ibn Abdullah and Bishr ibn al-Muhtafiz, from Abdullah ibn Umar, from the Prophet, may Allah bless him and grant him peace, that he said regarding silk: "Indeed, it is only worn by one who has no share [in the Hereafter]."