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The essential (fard) aspects of prayer are:

a. Standing (if possible)
b. Takbîrah al-Ihrâm
c. Reading Sûrah al-Fâtihah
d. Bowing
e. Rising from bowing
f. Prostrating
g. Sitting after prostrating
h. Reciting the tashahhud at the end of prayer
i. Sitting for the tashahhud at the end of prayer
j. The first taslîm
k. Doing everything in order
l. To do all of these completely and without haste

The obligatory (wâjib) aspects of prayer are as follows:

a. All other takbîrs
b. Offering tasbîh one time
c. Saying: ”Sami`a Allah liman hamidah, Rabbanâ laka al-hamd”
d. Saying “Rabbi-ghfir lî” between the two prostrations
e. The first tashahhud in a 3 or 4 unit prayer.
f. Sitting for the first tashahhud
g. Salutations on the Prophet

Everything else that we are supposed to do in prayer is recommended (sunnah).

And Allah knows best.

For more detail, refer to: al-Amâlî Sharh al-`Umdah by Sheikh Salman al-Oadah

Source: Islam Today