It was narrated from Abu Hurairah:
that the Messenger of Allah said: "Whoever has two wives and favors one of them over the other, he will come on the Day of Resurrection with one of his sides leaning." (AR)
English reference (AR): Vol. 3, Book 9, Hadith 1969 (AR)
Arabic reference (AR): Book 9, Hadith 2045 (AR)