Musannaf Ibn Abi Shayba 33:766

'Abdullah ibn Idris narrated to us, from Husayn, from Mujahid, from 'Ubayd ibn 'Umayr, who said: It used to be said: When winter comes, O people of the Qur'an, the night has become long for your prayer, and the day has become short for your fasting, so take advantage of it.