The Messenger of Allah said: "When a man has two wives and he is not just between them, he will come on the Day of Judgment with one side drooping." (Using translation from Tirmidhī 1141)
عَنِ النَّبِيِّ ﷺ قَالَ «إِذَا كَانَ عِنْدَ الرَّجُلِ امْرَأَتَانِ فَلَمْ يَعْدِلْ بَيْنَهُمَا جَاءَ يَوْمَ الْقِيَامَةِ وَشِقُّهُ سَاقِطٌ»