मज्झिम निकाय 3:70
SUJATO‘samādahaṁ cittaṁ assasissāmī’ti sikkhati, ‘samādahaṁ cittaṁ passasissāmī’ti sikkhati;
They practice like this: ‘I’ll breathe in immersing the mind in samādhi.’ They practice like this: ‘I’ll breathe out immersing the mind in samādhi.’