Muwatta Malik #296

Yahya related to me from Malik from Yahya ibn Said from Muhammad ibn Ibrahim that Abd ar-Rahman ibn Abi Amra al-Ansari said that Uthman ibn Affan came to the isha prayer and seeing only a few people in the mosque, he lay down at the back of the mosque to wait for the number of people to increase. Ibn Abi Amra went and sat down beside him and Uthman asked him who he was, so he told him. Uthman said, "What have you memorised of the Qur'an?", and he told him. Uthman said, "If someone is present at isha, it is as if he had stood in prayer for half a night, and if some one is present at subh, it is as if he had stood in prayer for a whole night.