1. To leave aside one or more Sunnah acts of Wudhu.
Nullifiers of Wudhu
1. Urination, defecation, passing wind. Allah says:
(Or any of you comes from answering the call of nature.) (5:6)
The Prophet (peace and blessing be upon him) said:
'Allah will not accept the prayer of one of you if he breaks the wind until he performs Wudhu.' (Agreed Upon)
2. Semen, Madthi and Wadi. The Messenger of Allah (peace and blessing be upon him) was asked about Madthi and he said: 'make Wudhu.'
Ibn Abbas (may Allah be pleased with both of them) said: 'One must make Ghusl for semen. As for Madthi and Wadi the Messenger of Allah (peace and blessing be upon him) said: 'Wash your penis, and make Wudhu like you would for prayers.'
3. Deep sleep, unconsciousness, intoxication and insanity. As for light sleep, in which one does not lose consciousness, it will not break his Wudhu.
4. Sexual intercourse.
5. Touching the penis directly. The Prophet (peace and blessing be upon him) said:
'Whoever touches his penis let him make Wudhu.' (Tirmidthi).
7. Eating camel's meat. The Prophet (peace and blessing be upon him) was asked: 'Shall we make Wudhu after eating camel's flesh?' He (peace and blessing be upon him) said: 'Yes.'
*Important note concerning 'camel's flesh'
*Eating camel's liver, fat, kidneys or intestines necessitates the renewal of Wudhu since it is similar to camel meat.
*Drinking camel's milk will not nullify one's Wudhu for the Prophet (peace and blessing be upon him) ordered a group of people to drink from its milk and did not order them to make Wudhu after that.
*It is best 'that a person make Wudhu after eating gravy of camel's meat, in order to be on the safe side.
Things that do not nullify Wudhu
1. Touching a woman directly. A'ishah, may Allah be pleased with her, said:
'A kiss will not nullify one's Wudhu, nor will it nullify one's fast.' (Baz'zaar).
2. Bleeding, whether it is from a wound, cupping and whether or not the blood that comes out is a lot or a little.
AI-Hasan, may Allah have mercy on him, said:
The Muslims continuously performed prayers and they had wounds. (Bukhari).
3. Vomit. This will not nullify one's fast, since no authentic, unambiguous textual proofs verify this.
4. Laughing during prayer. There is no authentic report to verify this.
5. Swearing (using bad words)
6. If you are not sure if you passed wind, then the rule is that you haven't unless you hear or smell it.