1 Samuel 6:7-12 NIV

7 "Now then, get a new cart1 ready, with two cows that have calved and have never been yoked.2 Hitch the cows to the cart, but take their calves away and pen them up.

References for 1 Samuel 6:7

8 Take the ark of the LORD and put it on the cart, and in a chest beside it put the gold objects you are sending back to him as a guilt offering. Send it on its way,
9 but keep watching it. If it goes up to its own territory, toward Beth Shemesh,3 then the LORD has brought this great disaster on us. But if it does not, then we will know that it was not his hand that struck us and that it happened to us by chance."

References for 1 Samuel 6:9

10 So they did this. They took two such cows and hitched them to the cart and penned up their calves.
11 They placed the ark of the LORD on the cart and along with it the chest containing the gold rats and the models of the tumors.
12 Then the cows went straight up toward Beth Shemesh, keeping on the road and lowing all the way; they did not turn to the right or to the left. The rulers of the Philistines followed them as far as the border of Beth Shemesh.