The son of Adam does not fill any vessel worse than his stomach. It is enough for the son of Adam to eat a few mouthfuls to straighten his back, but if he must (fill his stomach), then one third for his food, one third for his drink, and one third for his breath. [Ibn Maajah]

 «ما مَلَأ آدَمِيٌّ وِعَاءً شَرًّا من بطن، بِحَسْبِ ابن آدم أُكُلَاتٍ يُقِمْنَ صُلْبَه،ُ فإن كان لا مَحَالةَ، فَثُلُثٌ لطعامه، وثلث لشرابه، وثلث لِنَفَسِهِ».   (ابن ماجه)