SoHam

Soham means: I Am That. It is the natural vibration of the Self, which occurs spontaneously with each incoming and outgoing breath. By becoming aware of it on the conscious level by mentally repeating it in time with the breath (So when inhaling and Ham when exhaling), a yogi experiences the identity between his individual Self and the Supreme Self.

https://ocoy.org/how-to-meditate-an-introduction/

The important thing about Soham Yoga is that it really works. It only takes perseverance.