Musnad Abu Ya'la al-Mawsili 153:87

'Abdullah bin 'Abd al-Samad, or Salih bin 'Abd al-Samad his brother, narrated to us, Qasim narrated to us, from Sufyan, from 'Asim, from Salim, from Ibn 'Umar, who said: 'Umar came to the Messenger of Allah, may Allah bless him and grant him peace, seeking permission for the 'Umrah. He said: "O my brother, supplicate for us and do not forget us in your righteous supplication."