The Prophet Muhammad
(sallallahu alayhe wa sallam) said:
مَا مَلَأَ آدَمِيٌّ وِعَاءً شَرّاً مِنْ بَطْنِهِ
A person does not fill a
container worse than his stomache
بِحَسْبِ ابْنِ آدَمَ أَكَلَاتٌ يُقِمْنَ صَلْبَهُ
A few bites suffice the
son of Adam to strengthen his back (or keep himself fit)
فَإِنْ كَانَ لَا مَحَالَة
But if he must eat more
فَثُلُثٌ لِطَعَامِهِ
Then a third of the
stomach should be for his food
و ثُلُثٌ لِشَرَابِهِ
And a third for his drink
و ثُلُثٌ لِنَفَسِهِ
And a third for his breathing
Imam at Tirmidhee
collected it in his Sunan at Tirmidhi and said it was Hasan Saheeh.
Shaikh Albanee collected it in Irwaa al Ghaleel ( إرواء الغليل ) and said it had a
connected, authentic chain of narrators (إسناده صحيح متصل )
Find a hadeeth: http://dorar.net/enc/hadith/