Mishkat al-Masabih #696

As-Sa'ib b. Khallad, who was one of the Prophet's companions, said: A man led some people in prayer and spat in the direction of the qibla. Having seen this, God’s Messenger said to the people at the end of the prayer, “He must not lead you in prayer.” The man wanted to lead them in prayer some time afterwards, but they prevented him and told him what God's Messenger had said. He mentioned that to God’s Messenger, who replied, “Yes.” And I think he added, “You have harmed God and His Messenger.’’ Abu Dawud transmitted it.