Sahih Muslim 677
Sahih Muslim · Book 5: The Book of Mosques and Places of Prayer · It is recommended to say qunut in all prayers if a calamity befalls the Muslims – and refuge is sought from Allah (regarding that). It is recommended to say qunut in Subh at all times. And the clarification that it is to be said after raising the head from bowing in the final rak`ah, and it is recommended to say it out loud
حَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ ، حَدَّثَنَا هِشَامٌ ، عَنْ قَتَادَةَ ، عَنْ أَنَسٍ ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَنَتَ شَهْرًا يَدْعُو عَلَى أَحْيَاءٍ مِنْ أَحْيَاءِ الْعَرَبِ ثُمَّ تَرَكَهُ .
Anas reported that the Messenger of Allah (ﷺ) observed Qunut for one month invoking curse upon some tribes of Arabia (those who were responsible for the murders in Bi'r Ma'una and Raji'), but then abandoned it.