Musnad Ahmad 3:10

'Abd al-Rahman narrated to us, Sufyan narrated to us. And 'Abd al-Razzaq said: Sufyan informed us, from 'Uthman ibn Hakim, from 'Abd al-Rahman ibn Abi 'Amrah, from 'Uthman ibn 'Affan. 'Abd al-Razzaq said: From the Prophet, peace and blessings be upon him, who said: "Whoever prays the 'Isha' prayer and the Subh (dawn) prayer in congregation, it is as if he stood for the whole night." And 'Abd al-Rahman said: "Whoever prays 'Isha' in congregation, it is as if he stood for half the night, and whoever prays Subh in congregation, it is as if he stood for the whole night."