Musnad Abu Ya'la al-Mawsili 153:136

Abu Khaythama narrated to us, Waki’ narrated to us, Sufyan narrated to us, from ‘Asim, from Salim, from Ibn ‘Umar: That ‘Umar asked the Prophet, peace and blessings of Allah be upon him, for permission to perform ‘Umrah, and he gave him permission. He said, "O my brother, include us in your righteous supplication and do not forget us."