Buddhist Dictionary of Pali Proper Names by G P Malalasekera
arani sutta
Arani Sutta:There are five indriyas:those of ease,discomfort,happiness,unhappiness and indifference.Just as from the rubbing together of two sticks warmth and heat are produced,so,from their separation,warmth and heat,thus born,are quenched; similarly from contact,experienced as agreeable,arises the faculty of ease (sukhindriya),etc.S.v.211-13.