References – SN 43: Linked Discourses on the Unconditioned Saṁyutta Nikāya 43.1: Mindfulness Directed to the body 
Reflections by Ajahn Pasanno on jhāna and attainment. [Jhāna] [Conceit] [Concentration] // [Ajahn Chah] [Mindfulness of mind] [Suffering]
Sutta: SN 43.1: “Meditate [jhāyatha] bhikkhus, do not be negligent, lest you regret it later.”
Ānāpānasati: Mindfulness of In-and-Out Breathing [2005], Session 12, Excerpt 2
Readings from The Island by Ajahn Pasanno and Ajahn Amaro, Chapter 1, pp. 30-35. Read by Ajahn Amaro:
Nyanatiloka Bhikkhu, “Nibbāna,” Buddhist Dictionary, p. 105.
The Mind Like Fire Unbound by Ajahn Ṭhānissaro, p. 2.
Suttas: MN 26.13; SN 38.1; AN 10.60; Ud 3.10; AN 3.55; AN 6.55; SN 43.1-44.
Vinaya: Mahāvagga 1.5 (also occurs at SN 6.1 and MN 26.19).