Hazrat Zarah bin Thawb narrates that I asked Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) about fasting for a lifetime, so he replied that we used to consider such people among us as those who excelled in good deeds. He says, then I asked him about fasting one day and leaving it the next day, so he replied that such a person has not left any fast for the fasting person (as if he has kept all the fasts). And I asked him about keeping three fasts in every month, so he said that such a person has fasted for a lifetime and also left some (i.e., he has both fasted and left fasts).