Mahāparinibbāna Sutta 2.25.13

2.25.13

Yasmiṃ, ānanda, samaye tathāgato sabbanimittānaṃ amanasikārā ekaccānaṃ vedanānaṃ nirodhā animittaṃ cetosamādhiṃ upasampajja viharati, phāsutaro, ānanda, tasmiṃ samaye tathāgatassa kāyo hoti.

Sometimes the Realized One, not focusing on any signs, and with the cessation of certain feelings, enters and remains in the signless immersion of the heart. Only then does the Realized One’s body become more comfortable.