What breaks the wudu (ablution)

Ablution falls when its cause returns. Some causes are unanimous, others divide the schools: here are the main ones, as presented by the Mawsu'a.

What leaves the two passages breaks wudu

Everything leaving the two natural passages invalidates ablution by agreement of the scholars. For rare fluids such as madhiy and wadi, opinions differ: Abu Hanifa and Ash-Shafi'i require ablution, as for wind; Malik relies on the hadith:

There is no ablution except from a sound or a wind.hadith reported by Muslim

and requires nothing for these fluids. As for the blood of the woman with continuous bleeding (mustahada), it does not break her ablution: the Prophet told her to pray even if the blood stains the mat.

Sleep that breaks wudu

The jurists of the four schools agree: sleep invalidates ablution, especially deep or reclined sleep. The Prophet said: the eye is the tie-string of the water-skin; whoever sleeps should renew his ablution. However, one who dozes sitting, without support, need not repeat his ablution: the Companions waited for the prayer beside the Prophet while dozing without repeating it, and the school following Ibn 'Abbas reports that he even slept briefly before a prayer without a fresh ablution.

My eyes sleep but my heart does not sleep.al-Bukhari 1147, Muslim 738

Touching a woman: does it break wudu?

The Hanafis, Ahmad in one transmission and the choice of Ibn Taymiyya: touching a woman does not break ablution, except for deliberate desire-driven contact. 'Aisha reports that she slept in front of the Prophet while he prayed at night, and he nudged her feet with his to draw them in before his prostration (al-Bukhari 375, Muslim 512). He also kissed one of his wives then went to pray without a fresh ablution (Abu Dawud 179). Other jurists, on the contrary, require renewing ablution after any contact.

Practical note on breaking wudu

In case of doubt about a cause of nullification, the basic rule remains: certainty is not removed by doubt. If you are sure you were purified and doubt that you nullified, keep your purification and pray.