Riyad us Saliheen: Hadith 373

I sought permission of the Prophet (ﷺ) to perform 'Umrah. He granted me leave and said, "Dear brother! Do not forget us in your supplications". ('Umar added): This is something I would not exchange for the whole world.

Another narration is: He (ﷺ) said, "Include us, my dear brother, in your supplications."

[Abu Dawud and At-Tirmidhi, who categorized the Hadith as Hasan Sahih. Sheikh Salim Al-Hilali in his book "Bahjatun-Nazireen, Sharh Riyad-us- Saliheen" classifies it as "Da'if", the reason being that 'Asim bin 'Abdullah is "weak" in narration].