Ruling 928
Some of the obligatory components of the prayer are elemental (rukn), i.e. if one does not perform them – whether intentionally or mistakenly – the prayer is invalid. Some other obligatory components are not elemental, i.e. if they are omitted mistakenly, the prayer is not invalid. There are five rukns of the prayer:
1. Intention;
2. Takbīrat al‑iḥrām while standing;
3. Standing that is joined to rukūʿ, i.e. standing before rukūʿ;
4. Rukūʿ;
5. Two sajdahs in one rakʿah.
If a rukn is intentionally performed more than the prescribed number of times, the prayer is invalid. If it is done mistakenly, and if the additional act is a rukūʿ or two sajdahs in one rakʿah, then based on obligatory precaution, the prayer is invalid; otherwise [i.e. if the additional act is not a rukūʿ or two sajdahs in one rakʿah], it is not invalid.