References – Kd 2: The chapter on the observance day 
“Why did Jīvaka ask whether a virtuous lay follower is practicing for themselves or others (AN 8.26)?” Answered by Ajahn Pasanno. [Great disciples] [Lay life] [Virtue] [Compassion] [Buddhist identity] // [Culture/India] [Lunar observance days] [Teaching Dhamma]
Vinaya: Mahāvagga 2.1.1: Origin of Lunar Observance Days.