I heard the Messenger of Allah ﷺ say, "The son of Adam fills no vessel worse than his stomach. A few morsels are enough for the son of Adam to keep his back straight. If he must eat more, then let one third be for food, one third for drink, and one third for his breath."
سمعت رسول الله ﷺ يقول: ما ملأ ابن آدم وعاء شرا من بطن، حسب ابن آدم أكلات يقمن صلبه، فإن كان لا محالة، فثلت لطعام، وثلث لشراب، وثلث لنفسه.
Tirmidhi (2380), Ahmad (17186) narrated it, and Ibn Hibban (5236) and Hakim (4/331) graded it sahih, all of them through routes from Yahya bin Jabir Tai, from Miqdam bin Mad Yakrib, who related it. Ibn Majah (3349) also narrated it through another route from Maad Yakrib. Tirmidhi said, "This is a hasan sahih hadith." See its detailed sourcing in the book on asceticism. It contains a warning against excessive eating in general, and especially during the nights of Ramadan, because those nights are meant for worship and reciting the Quran, in accordance with the saying of the Prophet ﷺ, "Whoever stands in prayer during Ramadan out of faith and in hope of reward will have his previous sins forgiven." Yet people have introduced various kinds of food that were not known before, and have grown elaborate in preparing dishes at the expense of worship and the recitation of the Quran. And Allah is the one whose help is sought.