What Breaks Wudu
Wudu — the ritual washing required before prayer — stays valid until something specific breaks it, and knowing that list precisely matters more than it might seem, since praying without valid wudu invalidates the prayer itself. The clearest and most agreed-upon category is anything that exits from the front or back passage: urine, stool, gas, or any other discharge. This is the most common reason wudu needs renewing throughout an ordinary day and is treated the same way by every school of thought.
Deep sleep is the second major category, though the reasoning behind it is more specific than "falling asleep breaks wudu" as a blanket rule. The concern is loss of awareness — sleep that's deep enough that a person wouldn't necessarily notice if something had happened. A brief doze while sitting upright, where the person would likely still notice and wake at the slightest disturbance, is treated more leniently by many scholars than lying down and falling fully asleep, though practices differ across schools of thought on exactly where the line sits. Loss of consciousness through fainting, seizure, or intoxication is treated more strictly than ordinary sleep, since awareness there is more completely absent.
Direct skin-to-skin contact between spouses is a point of genuine difference between the schools rather than settled agreement — the Hanafi school generally holds that such contact alone does not break wudu unless it leads to the discharge described above, while the Shafi'i school takes a broader view that mere skin contact between a man and woman who are not mahram (not within permitted degrees of relation) does break it. This is one of the clearer examples of why "what breaks wudu" isn't a single universal list — it's worth knowing which school's rulings you're following, particularly on this point.
Touching one's own private parts directly, without a barrier of clothing, is treated by the majority of scholars as breaking wudu as well, based on a specific hadith on the topic, though again there is some difference of opinion on the details. When there's genuine uncertainty about whether wudu has been broken — a common experience, especially with gas — the general principle followed is that certainty is not removed by doubt: if wudu was definitely valid a moment ago, a vague uncertain feeling doesn't require starting over. Renewing wudu is only necessary when something is reasonably certain to have happened.