(Swaad) 38 : 44
وَخُذْ بِيَدِكَ ضِغْثًا فَاضْرِبْ بِهِ وَلَا تَحْنَثْ ۗ إِنَّا وَجَدْنَاهُ صَابِرًا ۚ نِعْمَ الْعَبْدُ ۖ إِنَّهُ أَوَّابٌ
And you take a bunch of grass and beat with it, you need not breach the promise, indeed We found him patient, what a blessed servant! Indeed he was repeatedly turning to Us.
When Prophet Ayyoob’s disease was serious and his wife had left him, he promised that he would beat her for hundred times. When he recovered from illness and his wife and his children joined him, the Lord commanded him to fulfill his promise by taking a bunch of grass containing a hundred petals and beating with them. See explanation 4: 100; 5: 89, and 18: 103-106.