صحيح مسلم

'Amir b. Sa'd b. Abu Waqqas reported: I wrote (a letter) to Jabir b. Samura (and it was sent) through my servant Nafi' asking him to inform me about something (pertaining to the Haud Kauthar). He wrote to me: I heard him (the Holy Prophet) say: I shall be there ahead of you at the Haud Kauthar.