Uttarajjhayana 14.19

14.19

no iṃdiyaggejjha amuttabhāvā amuttabhāvā vi ya hoi nicco |
ajjhatthaheuṃ niyayassa baṃdho saṃsāraheuṃ ca vayaṃti baṃdhaṃ ||

[The sons said:] “It cannot be grasped by the senses because of its formless nature; and because of its formless nature, it is eternal. / Bondage of the self is caused by internal factors, and they say bondage is the cause of the cycle of rebirth.