Musnad Ahmad 27:1498

Aswad ibn Amir narrated to us, Isra'il narrated to us, from Jabir, from Muslim al-Batin, from Sa'id ibn Jubayr, from Ibn Umar, who said: "I prayed behind the Messenger of Allah, may Allah bless him and grant him peace, three times, and he recited 'As-Sajdah' in the obligatory prayer."