Mantra for peace of mind in Hinduism is dedicated to Bhagavan Shiva and Vishnu together. The mantra should be chanted daily in the morning and evening. Here is the mantra for peace of mind in Hindi and English.
ॐ शिवाय शंकरी पीताम्बराया लक्ष्मी मनो सुखमे नमो नमः
Om Shivaya Shankari Pitambaraya Lakshmi Mano Sukhame Namo Namaha
Om Shivaya Shankari Pitambaraya Lakshmi Mano Sukhame Namo Namaha
The mantra should be chanted with a pure mind. You should try to remove all kinds of anger, hatred, jealousy, lust and intolerance from the mind. The mind should be like that of a new born baby.
The process of cleansing the mind might take several days or even months. But you should never give up.
The mantra should be chanted 108 times daily in the morning. After chanting the mantra one should read the Bhagavad Gita for 15 minutes.