Hafiz (; Arabic: حافظ, romanized: ḥāfiẓ, حُفَّاظ, pl. ḥuffāẓ, حافظة f. ḥāfiẓa), literally meaning "guardian" or "memorizer", depending on the context, is a term used by Muslims for someone who has completely memorized the Quran.
Some Muslims pray but with out understanding the message of Prayers and don't obey the Prophet (SAWA), like the Kharijites of that time and ISIS of today.
Real Prayer which purifies us is performed with humble obedience of Allah (SWT) and the Prophet (SAWA) and Ahlul Bayt (AS).
Taraweeh which is done nowby many Muslims was never performed by he Prophet Muhammad (SAWA), that is why you find that Umar Ibn Al-Khattab called it Bid'ah (Bukhari and Muslim).
The recommended Prayer is called Tahajjud which should be performed individually.
If some one forgets reciting Sura Al-Hamd, the Salaat is valid, but if he deliberately leaves reciting the Al-Hamd, then his Salaat is invalid.