Attributed to Thich Nhat Hanh
«Smile, breathe and go slowly.»
Misattributed
Verdict
It is not in Thich Nhat Hanh's work
A card-and-T-shirt motto that sums up his teaching but does not appear as his sentence in any locatable work; probably a condensation of several passages from Peace Is Every Step.
Source: Nhat Hanh, Thich. Peace Is Every Step: The Path of Mindfulness in Everyday Life. Nueva York: Bantam Books, 1991 (ISBN 9780553351392).
What they did say
Verified words of Thich Nhat Hanh
«Breathing in, I calm my body. Breathing out, I smile. Dwelling in the present moment, I know this is the only moment.»
Being Peace (1987), capítulo 1, «Suffering Is Not Enough»: la gatha de la respiración
«People usually consider walking on water or in thin air a miracle. But I think the real miracle is not to walk either on water or in thin air, but to walk on earth.»
The Miracle of Mindfulness (1975), capítulo 1, «The Essential Discipline»
«If you are a poet, you will see clearly that there is a cloud floating in this sheet of paper.»
The Heart of Understanding (1988), capítulo 1, «Interbeing»