This is from the fourteen mindfulness trainings from Thich Nhat Hanh, also called Thay. You can see them and more related information on the Deer Park Monastery website.
The Ninth Mindfulness Training: Truthful and Loving Speech
Aware that words can create suffering or happiness, I am committed to learning to speak truthfully and constructively, using only words that inspire hope and confidence. I am determined not to say untruthful things for the sake of personal interest or to impress people, nor to utter words that might cause division or hatred. I will not spread news that I do not know to be certain nor criticise or condemn things of which I am not sure. I will do my best to speak out about situations of injustice, even when doing so may threaten my safety.