Sahih Bukhari
Merits of the Helpers in Madinah (Ansaar)
Volume: 005 / Book Number: 058 / Hadith Number: 137
Narrated Anas bin Malik:
The Prophet said to the Ansar, "After me you will see others given preference to you; so be patient till you meet me, and your promised place (of meeting) will be the Tank (i.e. Lake of Kauthar)."