The phrase 生于忧患，死于安乐 (thrive in hardship, perish in comfort) comes from 《孟子·告子下》 (Mencius). 安乐 by itself is the literary term that pairs 'peace' with 'joy'.
usage
Slightly literary in tone. Common in compounds: 安乐死 (euthanasia — 'peaceful-and-happy death'), 安乐窝 (cozy nest / comfortable home).
