It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said during the Farewell Hajj: "I will surely kill the Amalekites with a battalion." Jibril (peace be upon him) said: Or (else) Ali bin Abi Talib (may Allah be pleased with him).
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11042