Musnad Abu Ya'la al-Mawsili 131:28

Muhammad ibn Isma'il ibn Abi Samina al-Basri narrated to us, 'Abd al-Wahhab ibn Najdah al-Homsi narrated to us, Muhammad ibn Shu'ayb ibn Shapur narrated to us, Sa'id ibn Khalid narrated to us, he said: I heard Anas ibn Malik saying: The Messenger of Allah (peace and blessings of Allah be upon him) said: "A day of guarding in the way of Allah is better than one of you standing [in prayer] among his family for a thousand years, fasting its days and standing [in prayer] its nights." The year is three hundred and sixty days; the day is a thousand years.