Rashi: The elder saddled it for Ish ha'Elokim. It says the pronoun (Lo) and afterwards the one to whom it refers (ha'Navi Asher Heshivo), like "va'Tir'ehu Es ha'Yeled" (Shemos 2:6) and similar verses.
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Was this the elder's donkey?
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Malbim: Yes. One Aveirah leads to another. After Ish ha'Elokim ate his fill, he accepted a gift. He should have judged that if he may not eat, all the more so he may not accept a gift
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