ENOfficial
‘Amr b. al-Hamiq told that he heard God's Messenger say, “He who grants a man security and then kills him will be given the banner of treachery on the day of resurrection.” It is transmitted in Sharh as-sunna.
Source: sunnah.com
Other translations
Arabic
وَعَنْ عَمْرِو بْنِ الْحَمِقِ قَالَ: سَمِعْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسلم يَقُول: «من أَمَّنَ رَجُلًا عَلَى نَفْسِهِ فَقَتَلَهُ أُعْطِيَ لِوَاءَ الْغَدْرِ يَوْمَ الْقَيَامَةِ» . رَوَاهُ فِي شَرْحِ السُّنَّةِ
sunnah.com