If I doubt my Wudu', should I pray or redo my Wudu', and what is the interpretation of "قطع الشك باليقين" (cut off doubt with certainty)?

If there is doubt about washing a limb after completing ablution, it should be disregarded, and there is no need to repeat the ablution. However, if the doubt occurs before completion, only the limb in question must be washed. This is based on the jurisprudential rule, "Certainty is not removed by doubt," which is derived from the Prophet's (peace and blessings be upon him) hadith: "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." This means that the default state of things remains until the contrary is certain. Therefore, if someone performs ablution and doubts whether they have invalidated it, they are not required to repeat the ablution. But if someone has invalidated their ablution and doubts whether they performed ablution afterward, they are considered to be in a state of impurity and must perform ablution.