بُلُوغُ الْمَرَامِ
Bulugh al-Maram 307
The Book of Prayer
وَعَنْ سَعْدِ بْنِ طَارِقِ الْأَشْجَعِيِّ - رضى الله عنه - قَالَ : { قُلْتُ لِأَبِي : يَا أَبَتِ ! إِنَّكَ قَدْ صَلَّيْتُ خَلْفَ رَسُولِ اَللَّهِ - صلى الله عليه وسلم -وَأَبِي بَكْرٍ , وَعُمَرُ , وَعُثْمَانُ , وَعَلَيَّ , أَفَكَانُوا يَقْنُتُونَ فِي اَلْفَجْرِ ? قَالَ : أَيْ بُنَيَّ , مُحْدَثٌ } رَوَاهُ اَلْخَمْسَةُ , إِلَّا أَبَا دَاوُدَ . [1]
Narrated Sa'd bin Tariq al-Ashja'i (RA): I said to my father, "You have prayed behind Allah's Messenger (ﷺ), Abu Bakr, 'Umar, Uthman, and 'Ali. Did they supplicate (with Qunut while standing) in the Fajr prayer?" He replied, "O my son, it is an innovation." [Reported by Al-Khamsah, except Abu Dawud].
Sunnah.com reference: Book 2, Hadith 193