Questioner: Is the hadith, ‘Fast and you will be healthy,’ authentic? If it isn’t how so?
Al-Albaani: This hadith differs totally from the one we mentioned before it, that last hadith about which we said that its chain of narration was weak and [along with that] the text itself was untrue [as well].
This hadith [however] is weak in terms of its chain of narration but correct in its meaning, ‘Fast and you will be healthy,’ as a hadith reported from the Prophet ﷺ according to the scholars of hadith its chain of narration is not authentic, but the state of affairs shows, and, before that, general hadith like his saying ﷺ, ‘It is enough for the Son of Adam to eat a few small bites that strengthens his spine. If he must have more, then let him fill a third with food, a third with drink and leave a third for his breathing,’ … so hadiths like this confirm, and as occurs in another hadith which has no basis whatsoever but which does contain fine wisdom, ‘Prevention is the best cure, and the stomach is the home of disease,’ for this reason, this hadith, ‘Fast and you will be healthy,’—its attribution to the Prophet ﷺ is not correct but, due to what we mentioned, its meaning is.
And what I mean when I say, ‘Its attribution to the Prophet ﷺ is incorrect,’ is that it is not allowed for a Muslim to say, ‘Allaah’s Messenger ﷺ said, ‘Fast and you will be healthy,’’ as you may have heard on some radio stations, this is not allowed. Why? Because the Prophet ﷺ said, ‘Whoever attributes to me something that I have not said, let him take his place in Hell.’
So it is not allowed for a Muslim to say a sentence, even if in and of itself it is a piece of wisdom and is acceptable in the view of other general, legislated proofs, [yet] it is [still] not allowed for a Muslim to say, ‘Allaah’s Messenger ﷺ said,’ unless it has, according to the scholars of hadith, been confirmed through the ways which establish the hadiths of the Prophet ﷺ.
Al-Hudaa wan-Noor, no. 692.