Nirāmisasutta

sn36.31:8.1 And what is equanimity not of the flesh?

sn36.31:8.2 It’s when, with the giving up of pleasure and pain and the disappearance of former happiness and sadness, a mendicant enters and remains in the fourth absorption, without pleasure or pain, with pure equanimity and mindfulness.

sn36.31:8.3 This is called equanimity not of the flesh.