Bhagwad Gita
Chapter 17, Verse 26
सद्भावे साधुभावे च सदित्येतत्प्रयुज्यते।प्रशस्ते कर्मणि तथा सच्छब्दः पार्थ युज्यते।।17.26।।
The word "Sat" is used to refer to reality and goodness; likewise, O Arjuna, the word "Sat" is used to refer to an auspicious act.