God’s Messenger صلى الله عليه و سلم did not mix food, and he did not eat alone. He did not eat fish and yogurt together, or drink milk with fish, and he did not eat anything sour with it or immediately after it. In fact, he never mixed in the same meal two hot foods, or two cold foods, and he never combined in any two dishes two viscous, costive, copragogue, diarrheic, pyknotic, or containing flaccid substances. Also, he did not eat any two dishes that dissolve as one upon eating, or clot apart in the stomach, and he did not combine an aperient dish with a costive dish, or a slow-digesting food with a fast-digesting one. Furthermore, he did not mix broiled and cooked food, or dry and fresh food, and he did not eat eggs with milk, or meat and milk, or hot food that has just come off the fire, or leftover food that was reheated, nor did he eat spoiled food, pickles, or food high in salt content.
In fact, combining any of the above categories of food may be harmful and can cause abscesses, hematolysis, or hepatitis among other illnesses, and they can drive the digestive system out of balance. Otherwise, and when possible, God’s Messenger صلى الله عليه و سلم balanced hot food with a little cold food to break its pungency, as he did when he ate fresh dates with cucumbers. He also ate dried dates with purified butter (Arb. heess), and he liked to drink extracts of dried dates soaked in water. This infusion prevents hydatid, or cystic build up that can develop in the tissues and liver, and which is sometimes caused by eating rich food.
God’s Messenger صلى الله عليه و سلم always insisted on having dinner, even if it were a handful of dried dates, and he used to say: “Neglecting dinner accelerates the aging process” (Reported by Imam al-Tirmithi). Abu Na’im narrated that God’s Messenger صلى الله عليه و سلم insisted on not going to sleep immediately after dinner, and he used to say: “Going to bed on a full stomach hardens one’s heart” (Reported by Imam Ibn Mãja). That is why knowledgeable physicians advise people to have a walk after dinner, even for as little as one hundred steps, and they suggest that sleeping on a full stomach is harmful. As for Muslim physicians, they advise either walking a few steps after dinner, or performing supererogatory (nafl) prayers before going to bed. This will help the food to settle in the stomach and the digestive process to ripen fully.
God’s Messenger صلى الله عليه و سلم also did not drink anything while eating, or after finishing his meal for half an hour at least, and particularly hot drinks or cold water, otherwise, the digestive process would be enfeebled, and could cause the food to spoil in the stomach. He also did not drink water when exhausted, after engaging in recreational exercise, after sexual intercourse, after a hot bath, or when suddenly walking up in the middle of his sleep, or after eating fruits, except after eating certain kinds of fruit when water can ease their digestion. All of these are accumulated habits that become second nature, and God willing, can be overcome gradually.