The best of it is to fast one day and not fast the next …
His statement, “The best of it is to fast one day and not fast the next,” means that the best voluntary fast is to fast one day and not fast the next.
If someone were to ask: Why did the Messenger, peace and blessings be upon him, not do this, when he was the one who proclaimed what is best, and he was the most fearful of Allah and most mindful of Him? We would say: because the Messenger, peace and blessings be upon him, was occupied with other acts of worship greater than fasting: calling people to Allah, and other duties that required his attention. Thus, the virtue of the call to prayer is authentically reported from him, and that the callers to prayer will have the longest necks on the Day of Resurrection (1). Yet he did not personally perform it, because he was occupied with other noble acts of worship and was unable to watch the sun as it rose, reached its zenith, and the like.
Likewise, concerning the man who entered and prayed alone, he said: “Who will give charity to this man?” One of his Companions then stood and prayed with him (2). No one should therefore say: Why did he not stand himself, since it was an act of charity and he was the foremost of people in doing good? The answer is that he was occupied with what was more important: teaching the people, speaking to them, winning their hearts, and the like.
In short, it should not be assumed that when the Messenger, peace and blessings be upon him, encouraged an act and explained that it was best, yet did not perform it himself, this reflected any shortcoming on his part—may Allah’s blessings and peace be upon him. Rather, he was occupied with what was more deserving and more important. This is why, when he was asked about fasting one day and not fasting for two days, he said: “Would that we were able to do that.” (3) That is, he was not