بُلُوغُ الْمَرَامِ
Bulugh al-Maram 309
The Book of Prayer
وَلِلْبَيْهَقِيِّ عَنْ اِبْنِ عَبَّاسٍ -رَضِيَ اَللَّهُ عَنْهُمَا- : { كَانَ رَسُولُ اَللَّهِ - صلى الله عليه وسلم -يُعَلِّمُنَا دُعَاءً نَدْعُو بِهِ فِي اَلْقُنُوتِ مِنْ صَلَاةِ اَلصُّبْحِ } وَفِي سَنَدِهِ ضَعْفٌ . [1]
Narrated Ibn 'Abbas (RA): Allah's Messenger (ﷺ) used to teach us a supplication to say in the Qunut of the morning prayer. [al-Baihaqi reported it and there is a weakness in its chain of narrators].
Sunnah.com reference: Book 2, Hadith 195