Nafi' reports: It was asked from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) about a place where filth and the like are thrown—can prayer be performed there? He replied: "When you have irrigated it three times, then you may perform prayer there." He narrated this as a marfu' (attributed to the Prophet) narration from the Prophet Muhammad (peace be upon him). However, there is disagreement regarding the chain of narration of this report. And Allah knows best.