Manava Dharmashastra 2.59

2.59

aṅguṣṭhamūlasya tale brāhmaṃ tīrthaṃ pracakṣate
kāyam aṅgulimūle 'gre devaṃ pitryaṃ tayor adhaḥ //

They call (the part) at the root of the thumb the tirtha sacred to Brahman, that at the root of the (little) finger (the tirtha) sacred to Ka (Pragapati), (that) at the tips (of the fingers, the tirtha) sacred to the gods, and that below (between the index and the thumb, the tirtha) sacred to the manes.