This quote is found everywhere, which isn’t surprising, since it reminds us of the importance of keeping the body in good health—something many of us neglect to do.
It’s from Buddha’s Little Instruction Book, where it’s “Our body is precious. It is our vehicle for awakening. Treat it with care.” (Note the use of “our” rather than “your” in the original.)
“Precious” is not, to the best of my knowledge, a term the Buddha ever used to describe the body.
However, he did indeed stress the importance of keeping the body healthy:
Reflecting properly, he takes alms-food. He does so not for enjoyment, not for vanity, not for improvement of the body, not for a better complexion, but only to sustain the physical body, to have just enough nourishment for maintaining life, to appease hunger and to carry out the Noble Practice of Purity. [He reflects thus:] ‘By this alms-food, I shall remove the existing discomfort and shall prevent the arising of new discomfort. I shall have just enough nourishment to maintain life and to lead a blameless life with good health.’ (Sabbasava Sutta)
But as you can see, the attitude to the body here is rather neutral. It’s not regarded as “precious” but is simply to be sustained, without attachment.
Seeing the body as precious would, for the Buddha, be taking us too close to what he called “intoxication” with health:
There are beings who are intoxicated with a [typical] healthy person’s intoxication with health. Because of that intoxication with health, they conduct themselves in a bad way in body… in speech… and in mind. But when they often reflect on that fact, that healthy person’s intoxication with health will either be entirely abandoned or grow weaker… (Upajjhatthana Sutta)
To counter this intoxication, the Buddha offered perspectives on the body that are less than flattering:
Behold this body — a painted image, a mass of heaped up sores, infirm, full of hankering — of which nothing is lasting or stable!
Fully worn out is this body, a nest of disease, and fragile. This foul mass breaks up, for death is the end of life.
As for the body being a vehicle for awakening, it could be argued that the Buddha came close to saying that in stressing the need for bodily mindfulness. For example in Dhammapada 293, he says:
But those who always practice well
do never what should not be done
and ever do what should be done;
mindful, clearly comprehending,
their pollutions out of existence go.
And even more clearly,
There is one thing that when cultivated and regularly practiced, leads to deep spiritual intention, to peace, to mindfulness and clear comprehension, to vision and knowledge, to a happy life here and now and to the culmination of wisdom and awakening. And what is that one thing? It is mindfulness centered on the body. (Anguttara Nikaya I 43)
The quote in question should probably be attributed to Jack Kornfield (along with many others that have been taken from Buddha’s Little Instruction Book and mis-attributed to the Buddha), but it may in turn be an adaptation of a verse from Tsongkhapa:
“The human body, at peace with itself, is more precious than the rarest gem. Cherish your body, it is yours this one time only. The human form is won with difficulty, it is easy to lose.”
The Buddha would certainly have agreed with Tsongkhapa about the rarity of human existence, but I doubt he would have used the word “precious” to describe the body.