Is the report of a trustworthy person indicating the occurrence of a ritual impurity to be accepted?

The correct view is that he is obligated to accept the report of a trustworthy person, and the claim that his report only conveys a probable opinion (zann) and does not elevate the certainty (yaqeen) of purity with a probable opinion of impurity (hadath) is baseless. If a trustworthy person were to report the occurrence of impurity in water, he would be obligated to accept his report. The report of a trustworthy person stands in the place of certainty (yaqeen) legally (shar'an) in many chapters of Islamic law.