Sayyiduna Ka'b bin Malik (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) said: "By the One in whose hand is my soul! With the poetry you say about them, it is as though you were showering them with arrows."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 21110