It is narrated from Hazrat Anas (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) recited Qunoot Nazilah after bowing in the Fajr prayer for a month and kept supplicating against some Arab tribes, then he abandoned it.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 13752