On one occasion, Sayyiduna Ali (may Allah be pleased with him) addressed the people from the pulpit and said: O people! I heard the Prophet (peace and blessings of Allah be upon him) say, "Prayer is not invalidated by anything except hadath (minor impurity)." And I will not feel shy to explain to you what the Prophet (peace and blessings of Allah be upon him) did not feel shy to explain: hadath means that a person passes wind.