It is narrated from Hazrat Khalid bin Aslam that Sayyiduna Umar bin Khattab (may Allah be pleased with him) once broke his fast in Ramadan, and that day it was cloudy. He thought that evening had come and the sun had set. Then a person came and said: O Commander of the Faithful! The sun has appeared. Sayyiduna Umar (may Allah be pleased with him) said: Its remedy is easy, we acted according to our assumption.

Imam Malik (may Allah have mercy on him) said: The remedy is easy, meaning that in compensation, we will keep a fast for one day, so the effort is very little and the remedy is easy.