Agniveshyagrihyasutra 2.6.1.4

2.6.1.4

aṅgulīmadhye daivaṃ tīrthaṃ aṅgulyagre ārṣaṃ tīrtham aṅguṣṭhatarjanyormadhye paitṛkaṃ tīrtham aṅguṣṭhamūlasyottarato rekhāsu brāhmaṃ tīrtham madhye agnitīrtham \

Between the fingers is the divine sacred spot; at the tip of the fingers is the sacred spot of the Ṛṣis; between the thumb and the forefinger is the ancestral sacred spot; at the base of the thumb, north of the lines, is the sacred spot of Brahmā; in the middle is the sacred spot of Agni.