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