Bhagavad Gita: Steady mind (Text 56, Ch2, Contents of Gita Summarized)

Dukhhesu anudvigna-manah sukhesu vigata-sprhah

Vita raga bhaya krodhah sthita-dhir munir ucyate

(Text 56, Ch2, Contents of Gita Summarized)

Meaning: One who is not disturbed in mind even amidst the threefold miseries or elated when there is happiness, and who is free from attachment, fear and anger, is called a sage of steady mind.