Sunan Ibn Majah, Volume 2, Book 5, Hadith 1243 (DarusSalam) ⓘ
It was narrated from Anas bin Malik that the Messenger of Allah used to recite Qunut in the Subh prayer, and he used to supplicate in it against one of the Arab tribes for a month, then he stopped doing so.
حَدَّثَنَا نَصْرُ بْنُ عَلِيٍّ الْجَهْضَمِيُّ، حَدَّثَنَا يَزِيدُ بْنُ زُرَيْعٍ، حَدَّثَنَا هِشَامٌ، عَنْ قَتَادَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ كَانَ يَقْنُتُ فِي صَلاَةِ الصُّبْحِ يَدْعُو عَلَى حَىٍّ مِنْ أَحْيَاءِ الْعَرَبِ شَهْرًا ثُمَّ تَرَكَ .
also referenced under: Hadith 1243 (Reference) & Book 5, Hadith 1301 (In-Book)