In this teaching, the Buddha instructed his young son, Rahula, with the seeds of some of his most important teachings.
Before you do anything, he told Rahula, ask yourself: Is what I intend to do here skillful or unskillful? Will it lead to well-being or harm? If it looks harmful, don’t do it. If it looks okay, go ahead and give it a try. While doing it, ask the same questions. If it turns out that it’s causing harm, stop. If not, continue with it. Then after you’ve done it, ask the same questions—Did it bring about well-being or harm?
Summary: Be aware of what we think, say and do. Reflect before, during and after. Through repeated reflection, we purify our thoughts, speech and actions.
https://www.accesstoinsight.org/tipitaka/mn/mn.061.than.html