Musnad Ahmad 30:2125

Khalaf ibn al-Walid narrated to us, he said: Ibn ‘Ayyash narrated to us, from Suhayl, from his father, from Abu Hurayrah, from the Prophet, may Allah bless him and grant him peace, that he said: "No servant conceals a servant in the world, except that Allah will conceal him on the Day of Resurrection."