Reference for Temurah 17:26

אי כתב הכי הוה אמינא

One 'a good' teaches us that even if one exchanges a good [animal] for a good [one], there is the punishment of lashes for substituting, and the other 'a good' teaches us that exchange takes effect only when the animal was 'good' originally, but where it was originally 'bad', exchange takes no effect.

Jastrow