Intention.
A person should offer prayers with the intention of Qurbat i.e. complying with the orders of the Almighty Allah. It is not, however, necessary that he should make his intention pass through his mind or should, for example, say: "I am offering four units of midday prayers Qurbatan illal (ah (i.e. to comply with the orders of Allah)"
Useful information:
OBLIGATORY ACTS RELATING TO PRAYERS
There are eleven obligatory acts for prayers:
(i) Niyyat (intention).
(ii) Qiyam (standing erect).
(iii) Takbiratul Ehram(saying Allahu Akbar while commencing the prayers).
(iv) Ruku' (bowing).
(v) Sajdatayn (two prostrations).
(vi) Qiraat (recitation of Surah al-Hamd and other surah).
(vii) Zikr (prescribed recitation while bowing and prostrating).
(viii) Tashahhud (bearing witness after completing the prostrations of the second unit).
(ix) Salam (salutation).
(x) Tartib (sequence) (xi) Muwalat (to perform the different acts of prayers in regular order without stop).