Apastambagrihyasutra 8.21.2

8.21.2

śucīnmantravato yo nigotramantrāsambandhānayugmām̐stryavarānanarthāvekṣo bhojayet \ 2 \

Let him feed, without regard of (worldly) purposes, pure Brâhmanas, versed in the Mantras, who are not connected with himself by consanguinity or by their Gotra or by the Mantras (such as his teacher or his pupils), an odd number, at least three.