Chapter 17 · The Three Kinds of Faith · Krishna said
Bhagavad Gita 17.26 — The meaning of Sat
सद्भावे साधुभावे च सदित्येतत्प्रयुज्यते। प्रशस्ते कर्मणि तथा सच्छब्दः पार्थ युज्यते ॥
sadbhāve sādhubhāve ca sadityetatprayujyate | praśaste karmaṇi tathā sacchabdaḥ pārtha yujyate ||
Meaning
O Partha, the word 'Sat' is used to mean reality and goodness, and it is also used for auspicious actions.