Fiqh-us-Sunnah - 2.97

Hadith 2.97.1

Intentionally leaving out an essenfial act or condition of the prayer without any valid excuse

Al-Bukhari and Muslim record that the Prophet sallallahu alehi wasallam told a bedouin who had not performed his salah well: "Return and pray for you have not prayed."
(This hadith was mentioned earlier.) Ibn Rushd writes: "There is an agreement that if one prays and he is not in a state of purity, it is obligatory for him to repeat the prayer, [that is true if the act was done] intentionally or out of forgetfulness.
Similarly, one who prays without facing the qiblah, intentionally or due to forgetfulness, [must repeat the salah]. In general, if any of the conditions for the correctness of the salah are absent, it becomes obligatory to repeat the salah. "