Nimittasutta
“Adhicittamanuyuttena, bhikkhave, bhikkhunā tīṇi nimittāni kālena kālaṁ manasi kātabbāni— kālena kālaṁ samādhinimittaṁ manasi kātabbaṁ, kālena kālaṁ paggahanimittaṁ manasi kātabbaṁ, kālena kālaṁ upekkhānimittaṁ manasi kātabbaṁ. Sace, bhikkhave, adhicittamanuyutto bhikkhu ekantaṁ samādhinimittaṁyeva manasi kareyya, ṭhānaṁ taṁ cittaṁ kosajjāya saṁvatteyya. Sace, bhikkhave, adhicittamanuyutto bhikkhu ekantaṁ paggahanimittaṁyeva manasi kareyya, ṭhānaṁ taṁ cittaṁ uddhaccāya saṁvatteyya. Sace, bhikkhave, adhicittamanuyutto bhikkhu ekantaṁ upekkhānimittaṁyeva manasi kareyya, ṭhānaṁ taṁ cittaṁ na sammā samādhiyeyya āsavānaṁ khayāya. Yato ca kho, bhikkhave, adhicittamanuyutto bhikkhu kālena kālaṁ samādhinimittaṁ manasi karoti, kālena kālaṁ paggahanimittaṁ manasi karoti, kālena kālaṁ upekkhānimittaṁ manasi karoti, taṁ hoti cittaṁ muduñca kammaniyañca pabhassarañca, na ca pabhaṅgu, sammā samādhiyati āsavānaṁ khayāya.
Basis
“Mendicants, a mendicant committed to the higher mind should focus on three bases from time to time: the basis of immersion, the basis of exertion, and the basis of equanimity. If a mendicant dedicated to the higher mind focuses solely on the basis of immersion, it’s likely their mind will incline to laziness. If they focus solely on the basis of exertion, it’s likely their mind will incline to restlessness. If they focus solely on the basis of equanimity, it’s likely their mind won’t properly become immersed in samādhi for the ending of defilements. But when a mendicant dedicated to the higher mind focuses from time to time on the basis of immersion, the basis of exertion, and the basis of equanimity, their mind becomes pliable, workable, and radiant, not brittle, and has become rightly immersed in samādhi for the ending of defilements.