Mudgalapurana 2.17.33

2.17.33

karmayuktaṃ ca sarvaṃ tatsvargabhogapradaṃ matam |
tadeva duḥkharūpaṃ tvaṃ putra jānīhi niścitam ||

And all that which is associated with [ritual] action is considered to bestow enjoyment in heaven;
know that that too, my son, is certainly of the nature of suffering.