Skandapurana 5.202.7

5.202.7

tathā pitāmahīpakṣe traya ete dvijottamāḥ..
mātāmahastatastasya pitā tasyāpi yaḥ pitā..7..

Likewise on the paternal grandmother’s side, these three [generations], O best of brahmins; / then his maternal grandfather, that man's father, and whoever was his father;