This was said by the Buddha, the Perfected One: that is what I heard.

“Mendicants, meditate observing the ugliness of the body. Let mindfulness of breathing be well-established internally in your presence. Meditate observing the impermanence of all conditions. As you meditate observing the ugliness of the body, you will give up desire for the body. When mindfulness of breathing is well-established internally in your presence, there will be no distressing external thoughts or wishes. When you meditate observing the impermanence of all conditions, ignorance is given up and knowledge arises.”

The Buddha spoke this matter. On this it is said:

“Observing the ugliness of the body, 
mindful of the breath, 
one always keen sees 
the stilling of all activities. 

That mendicant sees rightly, 
and when freed in regards to that, 
that peaceful sage, with perfect insight, 
has truly slipped their yoke.”

This too is a matter that was spoken by the Blessed One: that is what I heard.