Al-Mujadilah - 58:3

وَالَّذِينَ يُظَاهِرُونَ مِن نِّسَائِهِمْ ثُمَّ يَعُودُونَ لِمَا قَالُوا فَتَحْرِيرُ رَقَبَةٍ مِّن قَبْلِ أَن يَتَمَاسَّا ذَلِكُمْ تُوعَظُونَ بِهِ وَاللَّهُ بِمَا تَعْمَلُونَ خَبِيرٌ
[58:3]
And (as for) those who put away their wives by likening their backs to the backs of their mothers then would recall what they said, they should free a captive before they touch each other; to that you are admonished (to conform); and Allah is Aware of what you do.
But those who divorce their wives by Zihar, then wish to go back on the words they uttered,- (It is ordained that such a one) should free a slave before they touch each other: Thus are ye admonished to perform: and Allah is well-acquainted with (all) that ye do.
Those who put away their wives (by saying they are as their mothers) and afterward would go back on that which they have said, (the penalty) in that case (is) the freeing of a slave before they touch one another. Unto this ye are exhorted; and Allah is Informed of what ye do.