Hadith: Whoever has two wives and is inclined to one of them will come on the Day of Resurrection with one side of his body hanging down

عن أبي هريرة، عن النبي صلى الله عليه وسلم قال: «مَنْ كانت له امرأتان فَمَالَ إلى إحْداهُما جاء يومَ القيامةِ وشِقُّهُ مَاِئلٌ».
[صحيح] - [رواه أبو داود والترمذي والنسائي وابن ماجه والدارمي وأحمد]

Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "Whoever has two wives and is inclined to one of them will come on the Day of Resurrection with one side of his body hanging down."
Sahih/Authentic. - [Ibn Maajah]

Explanation

This Hadīth shows that it is mandatory to divide one's time among one's wives and that favoring one of them over the other is forbidden. The punishment for the man who treats his wives unjustly in this respect is that Allah will disclose him on the Day of Resurrection. He will come to the gathering place with one of his sides hanging down. This is an appropriate recompense, for one reaps what he sows. It is obligatory to treat one's wives fairly in matters that are controllable such as financial support, staying overnight, good treatment, and the like. However, this is not obligatory in uncontrollable matters such as love and inclination of the heart, since they are beyond one's power.