Reference for Bava Metzia 64:15

א"ל הא מני רבי יוסי הגלילי היא דאמר צער בעלי חיים לאו דאורייתא

Come and hear: In the case of an animal belonging to a heathen bearing a burden belonging to an Israelite, thou mayest forbear.<span class="x" onmousemove="('comment',' This refers to Ex. XXIII, 5: If thou seest the ass of him that hateth thee lying under his burden, and wouldst forbear to help him, thou shalt surely help with him, The Talmud disjoins the two phrases 'and wouldst forbear' (one word in Heb. we-hadalta) and 'thou shalt surely help him,' teaching that sometimes the first applies, i.e., one is permitted to withhold his aid, and sometimes the second, viz., 'thou shalt surely help him.' ');">¹³</span>

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