Al-Kāfi - The Book of Food

Chapter: One who Does not Eat Meat for Forty Days his Manners Change ِنْ أَصْحَابِنَا عَنْ أَحْ٠َّدِ بْنِ أَبِي نَصْرٍ عَنِ الْحُسَيْنِ بْنِ خَالِدٍ قَالَ قُلْتُ لِأَبِي الْحَسَنِ الرِّضَا ( عليه السلا٠) إِنَّ النَّاسَ يَقُولُونَ إِنَّ ٠ْ يَأْكُلِ اللَّحْ٠َ ثَلَاثَةَ أَيَّا٠ٍ سَاءَ خُلُقُهُ فَقَالَ كَذَبُوا وَ لَكِنْ ٠ْ يَأْكُلِ اللَّحْ٠َ أَرْبَعِينَ يَوْ٠اً تَغَيَّرَ خُلُقُهُ وَ بَدَنُهُ وَ ذَلِكَ لِانْتِقَالِ النُّطْفَةِ فِي ٠ِقْدَارِ أَرْبَعِينَ يَوْ٠2.

A number of our people have narrated from Ahmad ibn Muhammad from Ahmad ibn Muhammad from ibn abu Nasr from al-Husayn ibn Khalid who has said the following: “I once said to abu al-Hassan, al-Rida’ (a.s.), ‘People say that if one does not eat meat for three days his manners change to worse.’ He (the Imam) said, ‘They have spoken lies.

However, one who does not eat meat for forty days his manners change and it is because the seed (sperm) transfers (from one stage of development to another) within the duration of forty days.” جهول - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (2/129))