Yoga Sutras of Patanjali translated by Yogi Kalinath - Chapter 3, Verse 20
Pada 3, Sutra 20
Na ca tat saalambanam tasyaavisayee-bhootatvaat
But not the supporting object of the other’s mind as this is not the object of one’s integrated focus.
By meditating upon another mind’s content one can realize the state of mind of the other but not the intention or cause behind the exhibited state. In order to be able to reveal the intention or cause one would need to focus on the underlying reason for the emergence of those thoughts (mind content).
The Yogin who has stilled their own mind (the true meaning of purity) and can concentrate at will , are able to read the minds of others like an open book once they either focus on the other’s thoughts or the cause behind them.
We should always observe and be vigilant of our own motives as our mind is the Karma-making factory that ties us to the recurring wheel of Samsara.