one's word is bond
(one's) word is (one's) bond
One always keeps one's promises. I promise that I'll be there in time with the money for the deposit: my word is my bond.
one's word is one's bond
Fig. one's statement of agreement is as sound as a posting of a performance bond. Of course, you can trust anything I agree to verbally. My word is my bond. There's no need to get it in writing.