Highest Among All Gifts — Manusmriti 4.233

Among all gifts (water, food, cows, land, clothing, sesame, gold and ghee), the gift of sacred knowledge stands highest.

Teaching Is A Sacrifice — Manusmriti 3.70

Teaching is the offering to Brahman (sacred knowledge); water for the ancestors is the offering to forebears; the fire-offering is for the gods; the food-offering is for living beings; honouring guests is the offering to humankind.