When is the jurisprudential principle: "Certainty is not dispelled by doubt," applied, and what is the limit of doubt by which certainty is not dispelled?

The principle "certainty is not removed by doubt" applies to all chapters of Islamic jurisprudence and is considered one of the most important legal maxims. Its proof is the saying of the Prophet, peace and blessings be upon him: "If one of you finds something in his stomach and is unsure whether something came out of him or not, he should not leave the mosque until he hears a sound or perceives a smell."

Examples of this include: whoever is certain of purity and doubts impurity, he remains pure; and whoever doubts in his prayer, he should build upon what he is certain of.

The meaning of doubt is the equality of two opposing sides, or the absence of an indication for either. Certainty is not removed by doubt or by conjecture; rather, it is only removed by a certainty like it.