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

“Mendicants, there are these three feelings. What three? Pleasant, painful, and neutral feeling. Pleasant feeling should be seen as suffering. Painful feeling should be seen as a dart. Neutral feeling should be seen as impermanent. When a mendicant has seen these three feelings in this way, they’re called a noble mendicant who sees rightly, has cut off craving, untied the fetters, and by rightly comprehending conceit has made an end of suffering.”

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

“A mendicant who sees pleasure as pain, 
and suffering as a dart, 
and that peaceful, neutral feeling 
as impermanent 

sees rightly. 
And when freed in regards to that, 
that peaceful sage, with perfect insight, 
has truly slipped their yokes.”

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