1. Eating and drinking:

Ibn Al Mundhir said, “The people of knowledge are in agreement that it is forbidden to eat and drink while praying and all of the people of knowledge from whom we have memorised are in agreement that whoever eats or drinks intentionally during prayer must repeat it” [Al Awsat: 3/248].

2. Speaking intentionally when it is not for the purpose of prayer:

Ibn Al Mundhir said, “The people of knowledge are in agreement that the prayer of anyone who speaks intentionally in prayer, such that it is not for the purpose of prayer, is invalid” [Al Awsat: 3/234].

3. Laughing in prayer:

Ibn Al Mundhir said that there is scholarly agreement that laughing invalidates one’s prayer [Al Ijmā’: p.40]