Assalaamu alaykum wa rahmatullaahi wa barakaatuhu, Shaykhs. Is it true that the food of a generous person cures disease? If yes, is it permissible to eat more than one third if the food is of a generous person with the intention of wanting to get cured? I read about an incident about Imam Ash-Shaafi‘i in which he when to visit Imam Ahmad and he mentioned this or something similar to this and ate to maybe his fill, which I am not really sure of. Please quote evidence for the above question and about this incident. May Allaah reward you.

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger. 

There is a hadeeth that was narrated with this meaning.

Ibn ‘Umar, may Allah be pleased with him, narrated that the Prophet said, “The food of a generous person is a cure, while the food of a miserly person is an illness.” [Ibn ‘Adiyy and Ad-Daylami in Al-Firdaws]

As-Sakhaawi said about this hadeeth in Al-Maqaasid Al-Hasanah, “Our Shaykh said, ‘It is an objectionable hadeeth.’ Ath-Thahabi said, ‘It is a lie.’ Ibn ‘Adiyy said, ‘It is invalid from Maalik; there are unknown people in the chain of narrators and weak narrators, and it is not confirmed.’”

By ‘our Shaykh’ here, he means Ibn Hajar, as he said that in his book Lisaan Al-Meezaan.

The story that was reported by Imaam Ash-Shaafi‘i in this context included the daughter of Imaam Ahmad, and it is not authentic because Imaam Ahmad did not get married until after the death of Imaam Ash-Shaafi’i.

Allah knows best.