What Breaks the Prayer
Question :

What breaks the prayer?

Answer :

The following things invalidate the prayers:
A. Urinating and releasing wind or feces.
B. Turning the body fully away from the direction of the Ka'aba.
C. Any act that disturbs the prayers in the view of religious people, like eating or drinking.
D. Deliberate talking.
E. Deliberate laughing.
F. Putting one's hand on top of the other over the chest or stomach, if this is done so with the intention that it is part of the prayer.
G. Deliberately saying the word "Aameen" after finishing recitation of Surah al-Fatiha.
The said actions are proven by religious evidences to nullify the prayer, and we should submit to them even if we did not know the wisdom behind them.

Praying with Arms Across
Question :

Is it permissible for a Shia woman to pray with arms crossed on her breasts?

Answer :

If it leads to propagating against the right path or it is done with the intention that it is recommended, then it is prohibited in both cases. If it was with the intention of submission and humility, then it is permissible but not recommended.

Shaving Hair
Question :

If we do not shave or cut our pubic hairs and also underarm hairs, can we still offer prayers and will they be valid?

Answer :

It is recommended to remove the hair from both mentioned areas. However, the validity of the prayer is not affected by not removing hair from there.

Nose Touching the Mat
Question :

Is the prayer invalid if the nose directly touches the prayer mat?

Answer :

No, it does not.

Nullifying the Prayer
Question :

Is prayer annulled if one turns his head slightly to look to his left or right, or just moves his sight to the left or right?

Answer :

The prayer is not invalidated by this.

Invalidation of Prayer
Question :

If there are thoughts and images that come to mind during the prayer and I lose focus and concentration, is my prayer invalidated? What if such images and thoughts are forbidden, like the thought of a non-mahram lady? Do I need to repeat the prayer?

Answer :

The prayer is not invalidated by this.

Nullifing the Prayer
Question :

Is it forbidden to interrupt the prayer and invalidate it without cause?

Answer :

It is not permissible to nullify the obligatory prayer intentionally based on an obligatory precaution. It is permissible to do so for any recommended reason by the sharia or desired for worldly purpose.

The Prayers
Question :

What will happen if we think about things while we are praying?

Answer :

It is permissible and does not nullify the prayers.

Smoking Marijuana
Question :

Does smoking marijuana cause one’s prayers to not be accepter for 40 days, similarly to drinking alcohol?

Answer :

In some narrations, Imam Al-Sadiq (peace be upon him) stated that the prayers of a person that consumed intoxicants will not accepted for forty days, and if he dies during these forty days, he will be die as a death of an ignorant. If he repents during this time, it will be accepted.
This is not limited to alcoholic beverages, but applies to all intoxicants.