Muhsin bin Zabyan (may Allah have mercy on him) relates that he heard Abd al-Rahman bin Hassan say: A man from the tribe of Judham informed me that he heard Sayyiduna Malik bin Atahiyah (may Allah be pleased with him) say: I heard the Messenger of Allah (peace and blessings be upon him) say: "If you meet an 'ashshar (tithe-collector), kill him." The narrator said: By this is meant the one who collects charity (sadaqah) unlawfully.
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 16720