4.
The Discourse on Contact
305.
At Sāvatthī.
"Eye-contact, monks, is impermanent, subject to change, becoming otherwise;
Ear-contact...
nose-contact,
tongue-contact,
body-contact,
mind-contact is impermanent, subject to change, becoming otherwise.
Whoever, monks, thus believes in and resolves upon these phenomena, this one is called a faith-follower... etc.
headed for the highest enlightenment."
The fourth.