Bhagavad Gita 3.13यज्ञशिष्टाशिनः सन्तो मुच्यन्ते सर्वकिल्बिषैः।भुञ्जते ते त्वघं पापा ये पचन्त्यात्मकारणात् ॥

Those who, after performing the five great sacrifices, eat the remnants of the food are freed from all the sins committed by these five agents of insect slaughter, viz., (1) the pestle and mortar, (2) the grinding stone, (3) the fireplace, (4) the place where the waterpot is kept, and (5) the broom. These are the five places where injury to life is daily committed. The sins are washed away by the performance of the five MahaYajnas or great sacrifices which every Dvija(twicorn or the people belonging to the first three castes in Hindu society, especially the Brahmin) ought to perform1. DevaYajna Offering sacrifices to the gods which will satisfy them,2. BrahmaYajna or RishiYajna Teaching and reciting the scriptures which will satisfy Brahman and the Rishis,3. PitriYajna Offering libations of water to ones ancestors which will satisfy the manes,4. NriYajna The feeding of the hungry and the guests, and,5. BhutaYajna The feeding of the subhuman species, such as animals, birds, etc.