Padīpopamasutta

sn54.8:14.1 Now, a mendicant might wish:

sn54.8:14.2 ‘With the giving up of pleasure and pain, and the disappearance of former happiness and sadness, may I enter and remain in the fourth absorption, without pleasure or pain, with pure equanimity and mindfulness.’

sn54.8:14.3 So let them closely focus on this immersion due to mindfulness of breathing.