CC Ādi 2.79

taiche iṅha avatāra saba haila jñāta
kāra avatāra? — ei vastu avijñāta
Word for word: 
taiche — in the same way; iṅha — these; avatāra — incarnations; saba — all; haila — were; jñāta — known; kāra — whose; avatāra — incarnations; ei — this; vastu — thing; avijñāta — unknown.
Translation: 
“In the same way, all these incarnations were known, but whose incarnations they are was unknown.