What Invalidates the Prayer?
Question

Is there a set number of things that invalidate the prayer?
Praise be to Allah.The things that invalidate the prayer are well known, but the number differs according to differences among the jurists. They are as follows: 

Anything which invalidates Wudu , such as breaking wind or eating camel meat. 
Uncovering the `Awrah deliberately. But if it is uncovered by accident and what is uncovered is only a little, or if a lot becomes uncovered he covers it immediately, then the prayer is not invalidated. 
Turning away from the Qiblah to a large extent. 
Presence of impurity on one's body, clothes, or in the place where one is praying. If he notices it or remembers it during the prayer and removes it immediately, then his prayer is valid. Similarly, if he does not find out about it until after the prayer is over, his prayer is still valid. 
Excessive continuous movement during the prayer for no essential reason. 
Omitting one of the pillars (essential parts) of the prayer , such as bowing and prostration. 
Deliberately doing an extra pillar, such as bowing. 
Deliberately doing some pillars before others (changing the order). 
Deliberately saying the Salam before completing the prayer. 
Deliberately changing the meaning whilst reciting. 
Deliberately omitting one of the obligatory parts of prayer, such as the first Tashahhud . However, if a person forgets, his prayer is valid but he must do the prostration of forgetfulness (Sujud As-Sahw). 
Deciding (intending in the heart) to stop praying. 
Laughing out loud. Merely smiling does not invalidate the prayer. 
Deliberately speaking. If one speaks by mistake or out of ignorance of the ruling, the prayer is not invalidated. 
Intentional eating and drinking (while praying).  

References:

Dalil At-Talib li Nayl Al-Matalib by Shaykh Mar`i ibn Yusuf Al-Hanbali, p. 34)
Durus Muhimmah by Shaykh Ibn Baz. 

For more details, please see the following category: Things Which Invalidate the Prayer
And Allah knows best.