Jamieson, Fausset and Brown on Psalms 106:6

6. Compare 1Ki 8:47; Da 9:5, where the same three verbs occur in the same order and connection, the original of the two later passages being the first one, the prayer of Solomon in dedicating the temple.

sinned ... fathers--like them, and so partaking of their guilt. The terms denote a rising gradation of sinning (compare Psa 1:1).

with our fathers--we and they together forming one mass of corruption.