Salim narrates from his father (Abdullah bin Umar, may Allah be pleased with them both) that Sayyiduna Umar (may Allah be pleased with him) asked the Prophet (peace and blessings be upon him) for permission to perform Umrah, and he (peace and blessings be upon him) gave him permission and said: "O my brother, do not forget us in your supplications." The narrator (Umar) says: The Prophet (peace and blessings be upon him) said to me a word which I would not be pleased to exchange even for the whole world. Shu'bah says: Later I met Asim in Madinah and he narrated it to me, and in it he (peace and blessings be upon him) said: "O my brother, include us in your supplications."
(b) Salim bin Abdullah narrates from his father (Abdullah bin Umar, may Allah be pleased with them both), and he from Sayyiduna Umar (may Allah be pleased with him), that he (peace and blessings be upon him) said a word to me which I would not like to have the world in exchange for. The words "my brother" are present both at the beginning and at the end.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10315