In the Sahihan it is narrated that ‘ Abdullah bin Ja’far said, “ I saw the Messenger of Allah (sallalaahu alaihi wasallam) eat ripe dates with cucumbers.”
Dates are hot while cucumbers are cool, and each is suitable for the other and In addition neutralizes each others harm. This is a type of balancing off the harm of one substance by combining it with its opposite or antidote, and these are the goals that preventive science seeks to achieve. In fact, these are the goals that the science of medicine as a whole seeks to achieve.
Combining the foods or medicines with their antidotes or opposites makes the product milder and rids it of any harmful side effects. Consequently, the body will preserve its health, strength and wel lbeing.
The Prophet’s (sallallaahu alaihai wasallam) guidance on observing a diet as part of the cure
All types of cures and medicines contain either a certain diet or preventive measures. When one feels ill, he will need to rid the body from harmful substances and bodily wastes. These three elements are what medicine is all about.
Allah has said in the Qur’an :” And if you are ill or on a journey, or one of you comes after answering the call of nature, or you have been in contact with women ( by intimate relations) and you find no water, perform Tayammaum with clean earth [4:43]
Allah has saved the sick person from using water when there is a chance that it might harm him.
Ibn Majah narrated that Umm Al munthir bint Qays said,” The Messenger of Allah (sallallaahua alaihi wasallam) came along with Ali ( radiallahu anhu) who was then recovering from an illness. At that time, we had some hanging clusters of dates . The Messenger of Allah (sallallaahua alaihi wasallam) started eating from them and then Ali (radiallahu anhu) joined him. The Messenger of Allah kept saying to Ali (radiallahu anhu)” You are still recovering”, until Ali (radiallahu anhu) stopped eating’ I then made some barley and chard( similar spinach) and brought it to them. The Propeht (sallallaahua alaihi wasallam) said to Ali’ Eat from this food , it is more beneficial for you” In another narration, the Prophet (sallallaahua alaihi wasallam) said “ Eat from this food for it is more suitable in your condition [ Abu Dawood, Ahmed and Al-Hakim]
Know that the Prophet’s disallowing Ali from eating the hanging clusters of dates while still recupaerating from an illness is one of the best preventive measures. Fruits are not beneficial for sick or recovering patients as they get digested quickly at a time when the body is still fighting the ailment and it not strong enough to deal with an excess amount of food. Ripe dates in particular are heavy on the stomach at a time when the body is still resisting the ailment and removing its effects. Whatever part of the ailment that remains would either dissipate or re-intensify, depending on the condition of the body.
Excerpt from the book Prophetic medicine by Ibn Al Qayyim Al Jawziyy