Manusmriti
षण्णां तु कर्मणामस्य त्रीणि कर्माणि जीविका । याजनाध्यापने चैव विशुद्धाच्च प्रतिग्रहः ॥ ७६ ॥
But among the six acts (ordained) for him three are his means of subsistence, (viz.) sacrificing for others, teaching, and accepting gifts from pure men.
english translation
SaNNAM tu karmaNAmasya trINi karmANi jIvikA । yAjanAdhyApane caiva vizuddhAcca pratigrahaH ॥ 76 ॥
hk transliteration by Sanscript