The defendant must take an oath

وَقَالَ النَّبِيُّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «شَاهِدَاكَ أَوْ يَمِينُهُ». وَقَالَ قُتَيْبَةُ حَدَّثَنَا سُفْيَانُ عَنِ ابْنِ شُبْرُمَةَ كَلَّمَنِي أَبُو الزِّنَادِ فِي شَهَادَةِ الشَّاهِدِ وَيَمِينِ الْمُدَّعِي فَقُلْتُ قَالَ اللَّهُ تَعَالَى ‏{‏وَاسْتَشْهِدُوا شَهِيدَيْنِ مِنْ رِجَالِكُمْ فَإِنْ لَمْ يَكُونَا رَجُلَيْنِ فَرَجُلٌ وَامْرَأَتَانِ مِمَّنْ تَرْضَوْنَ مِنَ الشُّهَدَاءِ أَنْ تَضِلَّ إِحْدَاهُمَا فَتُذَكِّرَ إِحْدَاهُمَا الأُخْرَى‏}‏‏.‏ قُلْتُ إِذَا كَانَ يُكْتَفَى بِشَهَادَةِ شَاهِدٍ وَيَمِينِ الْمُدَّعِي، فَمَا تَحْتَاجُ أَنْ تُذَكِّرَ إِحْدَاهُمَا الأُخْرَى، مَا كَانَ يَصْنَعُ بِذِكْرِ هَذِهِ الأُخْرَىThe Prophet ﷺ said, (that the plaintiff must have) “Two witnesses, otherwise (the defendant) should take the oath.” Ibn Shubruma said, “When Abu Az-Zinad asked me my opinion about the verdict that one witness and the oath of the plaintiff are sufficient, I said, “Allah تعالى stated: ‘… And get two witnesses out of your own men. And if there are not two men (available), then a man and two women, such as you agree for witnesses, so that if one of them (two women) errs, the other can remind her…’ (V.2:282) I added, “If one witness and the oath of the plaintiff were sufficient, there would be no need for one of the two women to remind the other.”