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." (ES)
English reference (ES): Vol. 3, Book 9, Hadith 1969 (ES)
Arabic reference (ES): Book 9, Hadith 2045 (ES)