Saɱyutta Nikāya
5. Mahā-Vagga
54. Ānāpāna Saɱyutta
2. Ānanda or Dutiya Vagga
Connected Discourses on Breathing
Book 2: Ānanda
Sutta 19
The Course
Translated from the Pali by Bhikkhu Bodhi
[1][pts] " ... leads to the full understanding of the course."