Yahya related to me from Malik from Abd ar-Rahman ibn Harmala al- Aslami from Said ibn al-Musayyab that the Messenger of Allah, may Allah bless him and grant him peace, said, "What separates us from the hypocrites is being present at isha and subh. They cannot do it," or words to that effect.

Muwatta Malik Book 8, Hadith 5