Deut 22:10

22:10 an ox and a donkey together. The reason for this may be the impracticality both of making a donkey pull an ox’s load and of making an ox go at the faster donkey’s pace. Or, the contrast between clean animals (the ox) and unclean (the donkey, 14:1–8) may have served to remind Israel of her call to purity. Paul cites this verse in 2 Cor. 6:14, forbidding the fellowship of believers and unbelievers.