It was narrated from Yazid bin Al-Bara' that his father said: "I met my maternal uncle who was carrying a flag (for an expedition) and I said: 'Where are you going?' He said: 'The Messenger of Allah (ﷺ) is sending me to a man who has married his father's wife, and he has commanded me to strike his neck (kill him) and seize his wealth.'"
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا عَمْرُو بْنُ مَنْصُورٍ، قَالَ حَدَّثَنَا عَبْدُ اللَّهِ بْنُ جَعْفَرٍ، قَالَ حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ عَمْرٍو، عَنْ زَيْدٍ، عَنْ عَدِيِّ بْنِ ثَابِتٍ، عَنْ يَزِيدَ بْنِ الْبَرَاءِ، عَنْ أَبِيهِ، قَالَ أَصَبْتُ عَمِّي وَمَعَهُ رَايَةٌ فَقُلْتُ أَيْنَ تُرِيدُ فَقَالَ بَعَثَنِي رَسُولُ اللَّهِ صلى الله عليه وسلم إِلَى رَجُلٍ نَكَحَ امْرَأَةَ أَبِيهِ فَأَمَرَنِي أَنْ أَضْرِبَ عُنُقَهُ وَآخُذَ مَالَهُ .
sunnah.com