From Sahih Muslim (Hadith 1094):
Rabi'a b. Ka'b said:I was with Allah's Messenger (ﷺ) one night. and I brought him water and what he required. He said to me: Ask (anything you like). I said: I ask your company in Paradise. He (the Holy Prophet) said: Or anything else besides it. I said: That is all (what I require). He said: Then help me to achieve this for you by devoting yourself often to prostration
Reference: Muslim 1094