The fard (obligatory) prayer has shuroot (conditions), arkaan (pillars), and wajibaat (requirements). It also has things that are sunnah (recommended), and things that are makrooh (disliked). Then there are things that are generally permissible to be done in the salah. I will briefly discuss the conditions, pillars, and waajibaat as these are the things that are necessary for the validation of the salah and for this reason a believer should not remain ignorant about them. If time permits I may briefly mention the other aspects of the salah. However my intention is to help others meet the basic requirements of their worship, so I would like to focus on what is priority.
Conditions: The conditions are prerequisites that have to be met before a person begins their salah. They have to be met in order for the salah to be valid. If a person does not fulfill anyone of these conditions for any reason, whether it be due to ignorance, forgetfulness, or intentionally does not do them, then their salah is invalid. Once a person realises that he/she missed a condition they should repeat that salah, even if a long period passes.
The conditions of Salah are 9. They are:
1. Al-Islaam (Salah is only accepted from a Muslim)
2. Al-‘aql (Sanity. The insane is not held accountable for his/her actions)
3. Al-tamyeez (puberty)
4. State of purity (having wudu or taking a ghusl to remove ritual impurity)
5. Removal of filth (clothing should be free from impurities)
6. Covering the awrah
7. Commencement of time (The salah must be prayed in its proper time and not a minute before)
8. Facing the direction of the qiblah
9. An-niyah (the intention for the prayer being prayed should be present)
Pillars: The pillars of the salah are those things that are necessary for the validation of the salah. If any pillar is left out due to ignorance, forgetfulness, or deliberate omission the Salah becomes invalid. The prostration of forgetfulness* cannot compensate for the omission of a pillar. The pillar has to be done or the salah has to be repeated, even if a long time passes.
The arkaan (pillars) of Salah are 14. They are:
1. Standing (An able person must stand while praying)
2. Takbiratul Ihraam [ the opening takbeer (i.e. the first Allaahu akbar)]
3. The recitation of Al-faatihah
4. The rukoo’ (the bowing position)
5. Rising up from the rukoo
6. Sajuud on the 7 bones (1. forehead & nose, 2&3. both palms, 4&5. both knees, 6&7. both feet – all must touch the floor during prostration)
7. Coming up from the prostration position
8. Sitting calmly between the two prostrations
9. Being tranquil and calm during every pillar position
10. The pillars should be done in order (e.g. rukoo before sujood etc.) 11. The last tashahud (at-tahiyaat) [In fajr the last is also the first]
12. Sitting during the last tashahud
13. Sending the salaat and salaam upon the nabi salallaahu ‘alayhi wasalam (saying ‘Allaahumma salli ‘ala Muhammad ….) in the last tashahud
14. The two tasleems (saying ‘assalaamu ‘alaykum wa rahmatullaah to the right and then to the left)
* Prostration of forgetfulness (sajuudu as-sahw) is the two prostrations made at the end of the prayer to compensate for mistakes done within the prayer. The mistake of leaving a pillar cannot be made up by simply making these two prostrations.
Waajibaat: The waajibaat of the salah are those things that must be done within the salah and if they are left out due to ignorance or forgetfulness the salah is still valid. If they are left due to these reasons they can be compensated for with the prostration of forgetfulness. However, if they are deliberately omitted then the salah is invalid.
The waajibaat of the Salah are 8. They are:
1. All of the takbiraat except takbiratul ihram [All the sayings of Allaahu akbar except the first one (first one is a pillar)]
2. Saying: Subhaana rabiyal ‘atheem (at least once) in rukoo/bowing position
3. Saying: sami Allaahu liman hamidah
4. Saying: rabbanaa wa lakal hamd
5. Saying: Subhaana rabbiyal ‘ala (at least once) in sujood
6. Saying: rabighfirlee (at least once) while sitting between the two prostrations
7. The first tashahud (at-tahiyaat) [in fajr the first is a pillar, in the others prayers they are wajibaat]
8. Sitting down during the first tashahud
If a person remembers that they forgot one of these wajibaat while still praying, then they only have to make the two prostrations for forgetfulness. If they remember a long time after they already completed the prayer then inshallaah they are excused.
Summarising:
Conditions are prerequisites for the salah. A person is not excused from them regardless if he was ignorant of its obligation, or if he forgot, or if he deliberately left it.
Pillars are those things that a person is not excused from due to ignorance, forgetfulness or deliberate omission. The prostrations for forgetfulness cannot compensate for the omission of a pillar.
Wajibaat are those things that if a person omits them due to not knowing of its obligation or forgetting it, then the salah remains valid, and the prostration for forgetfulness can compensate for what was left out. Deliberate omission, however, invalidates the salah.
UPDATE: If a person remembers that they forgot one of the waajibaat before they move on to the next position, then they should return and fulfil what they left, and then they do not have to make sujuudus-sahw at the end. But if they move on to the next position and then remember, it is now FORBIDDEN to return. In this case the person moves on and makes sujuudus-sahw before tasleem.
Example: a person is about to stand after the second raka’a and while they are getting up they remember they forgot to make tashahud, they should sit back down and say the tashahud. If they stand up completely erect and then remember, they should not return. They make sujuudus-sahw at the end before the tasleem.
http://islamicbasics.wordpress.com/2...and-waajibaat/