Sahih Muslim Book 30, Hadith Number 5685.

Chapter : The cistern of our Apostle (may peace be upon him) and its characteristics.

‘Aisha reported: I heard Allah’s Messenger (may peace be upon him) say in the company of his Companions: I would be on the Cistern waiting for those who would be coming to me from amongst you. By Allah, some persons would be prevented from coming to me, and I would say: My Lord, they are my followers and people of my Umma. And He would say,: You don’t know what they did after you; they had been constantly turning back on their heels (from their religion).