וְעַתָּ֗ה קְח֨וּ וַעֲשׂ֜וּ עֲגָלָ֤ה חֲדָשָׁה֙ אֶחָ֔ת וּשְׁתֵּ֤י פָרוֹת֙ עָל֔וֹת אֲשֶׁ֛ר לֹא־עָלָ֥ה עֲלֵיהֶ֖ם עֹ֑ל וַאֲסַרְתֶּ֤ם אֶת־הַפָּרוֹת֙ בָּעֲגָלָ֔ה וַהֲשֵׁיבֹתֶ֧ם בְּנֵיהֶ֛ם מֵאַחֲרֵיהֶ֖ם הַבָּֽיְתָה׃
Rashi on I Samuel
Which have not borne a yoke. All this is for the test. Since these cows are not capable of pulling [a load], and furthermore, they will yearn for their young. If the Ark will have the power to enable them to pull it by themselves, we shall know that He brought this upon us.