It is narrated from Abu Mijlaz (may Allah have mercy on him) that the qunut supplication in the morning (Fajr) prayer was mentioned before him, and he related that the Messenger of Allah (peace and blessings be upon him) sent a man to such-and-such a tribe and instructed him: "Go and see; if they have called the adhan (that is, they have accepted Islam), leave them and go on to such-and-such a tribe." When that messenger reached them and began questioning them, a man went inside, put on his armour, that is, his weapons, came out, struck the messenger of the Messenger of Allah (peace and blessings be upon him) with a spear and threw him to the ground (and martyred him). At that moment the messenger of the Messenger of Allah (peace and blessings be upon him) implored: 'Allahumma inni rasulu rasulika, iqra' alayhi minni al-salam' (O Allah, I am the envoy sent by Your Messenger; convey my greeting of peace to him from me). (Meanwhile, in Madinah,) the Prophet (peace and blessings be upon him) suddenly said: "Wa alaykum al-salam (and upon you be peace)." The people present there said: O Messenger of Allah, we have not seen anyone here (so whom are you answering)? He (peace and blessings be upon him) said: "So-and-so has been martyred, and he has sent me the greeting of peace." After this incident, the Prophet (peace and blessings be upon him) stood for a month in the last part of the Fajr prayer to supplicate against them, saying: 'Allahumma alayka bi-Bani Usayyah, asaw rabbahum, wa alayka bi-Bani Dhakwan' (O Allah, seize Banu Usayyah, for they have disobeyed their Lord, and seize Banu Dhakwan as well). The narrator said: Then he (peace and blessings be upon him) abandoned it, and apart from this incident he (peace and blessings be upon him) never recited the qunut.
This narration is mursal.
Hadith Referenceالمطالب العالية بزوائد المسانيد الثمانية / صفة الصلاة / 484
Hadith Gradingمحدثین:إسناده مرسل
Hadith Takhrij«حکم الحدیث المطالب العالیہ محققاً تنسیق د. سعد بن ناصر بن عبد العزيز الشَّثري- مکتبہ شاملہ :قال ابن حجر: مُرْسَلٌ . » «انفرد به المصنف من هذا الطريق»