Fearless Simplicity(中譯大圓滿生活), p.85-86止:修學
The correct practice of shamatha further and further strengthens [the] alert quality. It transforms into an increasing sense of being awake. Meanwhile, the mindful quality becomes more and more mindful, so that it requires less and less effort. You are just naturally mindful, naturally present. And the sense of being settled, of dwelling in the nowness, becomes more and more of the same identity as the alertness, until finally the alertness pulls this state into something that is no longer just shamatha: it has become vipashyana, the state of seeing clearly. The Mahamudra teachings say that when the division between stillness and thought occurrence falls away, this is the recognition of one-pointedness. This one-pointedness is actually shamatha.
Fearless Simplicity, p. 67