Agnipurana 357.6

357.6

sipthastha madhyamanaro mipvasmascottamaḥ pumān /
ta ātāṃ antātmane mukhyaḥ thāsāthāṃ dhvañca madhyamaḥ //

Sip, thas, tha are the middle (second) person; mip, vas, mas are the highest (first) person. / Ta, ātām, jha (anta) are the main [endings] for the ātmanepada; thās, āthām, and dhvam are the middle;