It is reported from Sayyiduna Anas (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) supplicated in qunut against those tribes for a month, then abandoned it; but in the morning prayer he always continued to recite qunut until he departed this world.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3104