Sunan Ibn Majah Book 20, Hadith 2607

حَدَّثَنَا إِسْمَاعِيلُ بْنُ مُوسَى، حَدَّثَنَا هُشَيْمٌ، ح وَحَدَّثَنَا سَهْلُ بْنُ أَبِي سَهْلٍ، حَدَّثَنَا حَفْصُ بْنُ غِيَاثٍ، جَمِيعًا عَنْ أَشْعَثَ، عَنْ عَدِيِّ بْنِ ثَابِتٍ، عَنِ الْبَرَاءِ بْنِ عَازِبٍ، قَالَ مَرَّ بِي خَالِي - سَمَّاهُ هُشَيْمٌ فِي حَدِيثِهِ الْحَارِثَ بْنَ عَمْرٍو - وَقَدْ عَقَدَ لَهُ النَّبِيُّ صلى الله عليه وسلم لِوَاءً فَقُلْتُ لَهُ أَيْنَ تُرِيدُ فَقَالَ بَعَثَنِي رَسُولُ اللَّهِ صلى الله عليه وسلم إِلَى رَجُلٍ تَزَوَّجَ امْرَأَةَ أَبِيهِ مِنْ بَعْدِهِ فَأَمَرَنِي أَنْ أَضْرِبَ عُنُقَهُ ‏.‏

It was narrated that Bara bin Azib said:“My maternal uncle passed by me - (one of the narrators) Hushaim named him in his narration as Harith bin Amr - and the Prophet (ﷺ) had given him a banner to carry. I said to him: 'Where are you going?’ He said: 'The Messenger of Allah (ﷺ) has sent me to a man who married his father's wife after he died, and has commanded me to strike his neck (i.e. execute him).”