Musannaf Ibn Abi Shayba 3:1045

Abu Khalid narrated to us, from Muhammad ibn Ishaq, from Abu Bakr ibn Amr ibn Hazm, from Amr ibn Sulaym, from Abu Qatadah, that the Prophet, peace and blessings of Allah be upon him, said: "Give the mosques their right." It was said: "And what is their right?" He said: "Two rak'ahs before you sit down."