Arabic text
عن عاصم قال: سألتُ أنساً رضي الله عنه عن القُنُوت، قال: قبل الركوع، فقلت: إن فلاناً يزعم أنك قلت بعد الركوع؟ فقال: كَذَبَ، ثم حَدَّثَنَا، عن النبي صلى الله عليه وسلم : «أنه قنت شهراً بعد الركوع، يدعو على أحياء من بني سليم»، قال: «بعث أربعين -أو سبعين يشك فيه- من القراء إلى أناس من المشركين»، فعرض لهم هؤلاء فقتلوهم، وكان بينهم وبين النبي صلى الله عليه وسلم عهد، «فما رأيته وجد على أحد ما وجد عليهم».
Translation
‘Āsim reported: I asked Anas about the Qunūt (invocation in the prayer). Anas said: "It should be recited before Rukū‘." I said: "So-and-so claims that you said it should be recited after rising from Rukū‘." He replied: "He is mistaken." Then Anas narrated to us that the Prophet invoked evil on the tribe of Banu Sulaym for one month after rising from Rukū‘. He then said: "The Prophet (may Allah's peace and blessings be upon him) sent 40 or 70 reciters (men well versed in the knowledge of the Qur'an) to some pagans, who killed them, even though there was a peace pact between them and the Prophet (may Allah's peace and blessings be upon him). I never saw the Prophet hating anyone as much as he hated those pagans."
Explanation
This Hadīth clarifies the permissibility of supplicating during calamities. It is to be performed after rising from Rukū‘, according to the way the Prophet (may Allah's peace and blessings be upon him) did when Banu Sulaym broke the covenant between them and the Muslims by killing 40 or 70 of the reciters whom the Prophet had sent to them. The Prophet supplicated against them for a month after rising from Rukū‘.
Source: HadeethEnc.com