Sunan Ibn Majah 4301

It was narrated from Abu Sa’eed Al-Khudri that the Prophet (ﷺ) said:“I have a Cistern, (as large as the distance) between the Ka’bah and Baitul-Maqdis (Jerusalem). (It is) whiter than milk, and its vessels are the number of the stars. I will be the Prophet with the most followers on the Day of Resurrection.”