Al-Rabia’ ibn Sulayman reported: Al-Shafi’i, may Allah have mercy on him, said, “I have not satiated myself for sixteen years, as I have cast fullness aside. For satiety puts heaviness in the body, hardens the heart, causes loss of intelligence, induces sleepiness, and weakens the performance of the worshiper.”
Source: Ādāb al-Shāfiʻī wa Manāqibuh 1/78
عن الرَّبِيع بْن سُلَيْمَان قَالَ قَالَ الشَّافِعِيُّ رضي الله عنه مَا شَبِعْتُ مُنْذُ سِتَّ عَشْرَةَ سَنَةً إِلا شُبْعَةً اطَّرَحْتُهَا يَعْنِي فَطَرَحْتُهَا لأَنَّ الشِّبَعَ يُثْقِلُ الْبَدَنَ وَيُقَسِّي الْقَلْبَ وَيُزِيلُ الْفِطْنَةَ وَيَجْلِبُ النَّوْمَ وَيُضْعِفُ صَاحِبَهُ عَنِ الْعِبَادَةِ
1/78 آداب الشافعي ومناقبه