Musannaf Ibn Abi Shayba 3:5422

Waki’ narrated to us, he said: Yahya bin Muslim al-Hamdani narrated to us, from Sa’id bin ‘Amr al-Qurashi, who said: I followed ‘Abdullah bin ‘Umar to learn from him, and I did not see him praying the *subha* (voluntary prayer). And whenever he saw them praying it, he would say: "Of the best things they have innovated is this *subha* of theirs."