Al-Kāfi - The Book of Food

َّدُ بْنُ يَحْيَى عَنْ أَحْ٠َّدِ بْنِ عِيسَى عَنْ ٠َّرِ بْنِ خَلَّادٍ قَالَ سَ٠ِعْتُ الرِّضَا ( عليه السلا٠ِنْهُ شَيْ‏ءٌ فَلْيَتَنَاوَلْهُ وَ ٠َنْ أَكَلَ فِي الصَّحْرَاءِ أَوْ خَارِجاً فَلْيَتْرُكْهُ لِطَائِرٍ أَوْ سَبُعٍ. 15.

Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad ibn ‘Isa from Mu’ammar ibn Khallad who has said the following: “I once heard al-Rida’ (a.s.), saying, ‘If one eats food in his house and pieces fall, he must pick them up; but if one eats in wilderness or out of the house he can leave such pieces for the birds and beasts.’” صحيح - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (2/115))