Musannaf Ibn Abi Shayba 4:186

Abu Mu'awiyah narrated to us, from al-A'mash, from Zayd ibn Wahb, who said: Drinking vessels were brought out from the house of Hafsa while there were clouds in the sky. They thought that the sun had set, so they broke their fast. They had not waited long before the clouds cleared, and behold, the sun was rising. Umar said: "We have not inclined toward sin."