What should be learned of the Qur’aan and hadeeth?

Some Islamic knowledge is
obligatory for every accountable individual to learn. This is called fard
‘ayn (individual obligation). The definition is: if it has to do with an act
of worship that he is obliged to do, or a transaction that he wants to
engage in (then he must learn it). 

And some knowledge is
obligatory for the ummah in general: if some of them do it in the required
manner then the rest are absolved of responsibility, otherwise all of those
who are able to do it are sinning. This is called fard kifaayah (communal
obligation). 

Memorizing Qur’aan and
hadeeth comes under the leading of the latter. The ummah is obliged to
preserve the Book of Allaah and the hadeeth of His Messenger, whether in
their hearts or on paper, so that nothing of the two sources of legislation
will be lost. Imam al-Nawawi (may Allaah have mercy on him) said in the
introduction to Sharh al-Muhadhdhab (1/51): The second type – i.e.,
of Islamic knowledge – is a communal obligation (fard kifaayah), which means
acquiring that Islamic knowledge which is essential for the people to
establish their religion, such as memorization of Qur’aan and hadeeth, and
their sciences, and usool al-fiqh.  

As for memorization of
Qur’aan and hadeeth as an individual obligation – i.e., that which the
accountable Muslim is required to memorize – he is not obliged to memorize
any of that by heart, he only has to memorize that without which prayer is
not valid. Al-Faatihah has to be learned by every accountable person, i.e.,
he has to learn how to recite it properly. If he learns it by heart that is
good; if he does not learn it by heart then he must read it from the Mus-haf
or a piece of paper and the like. 

Al-Nawawi said in
al-Majmoo’ (3/335): Our companions said: If a person is not able to
recite al-Faatihah then he should acquire the ability to do so by learning
it, or acquire a Mus-haf from which he can read it, by buying it or renting
it or borrowing it. If he is praying at night or in the dark, then he must
acquire a lamp if he can. If he refuses to do that when he is able to do it,
then he is sinning and must repeat every prayer that he offered before he
learned al-Faatihah. Our evidence is the well-known shar’i principle that
everything without which an obligatory duty cannot be performed, when it is
within a person’s capabilities, is obligatory. End quote. 

In Kashshaaf al-Qinaa’
(1/34) by al-Bahooti (may Allaah have mercy on him) it says: “The ignorant
person” i.e., the one who cannot recite al-Faatihah well “must learn it”
because it is obligatory in prayer, so he has to learn it if he is able to,
as a condition (of prayer). “If he does not do that” i.e., if he does not
learn al-Faatihah, “when he is able to do it, then his prayer is not valid”
because he has failed to do an obligatory action when he was able to do it.
End quote. 

Mustafa al-Ruhaybaani
al-Hanbali said in Mataalib Ooli al-Nuha (1/432): The ignorant person
must learn al-Faatihah because it is obligatory in prayer, so he must learn
it if he is able, as it is a condition of prayer. End quote. 

The same applies to
hadeeth: Muslim men and women are not required to memorize any of them, but
it is essential to learn that without which the prayer is invalid, such as
the hadeeth which describes the wording of the tashahhud to be recited in
prayer. Ibn Qudaamah (may Allaah have mercy on him) said in al-Mughni
(1/315): The minimum that is acceptable is Al-Tahiyyaatu Lillaahi
wa’l-salaamu ‘alayka ayyhuha’l-nabiyyu wa rahmat-Allaah, al-salaamu ‘alayna
wa ‘ala ‘ibaad Illaah il-saaliheen, ashhadu an la ilaaha ill-Allaah wa
ashhadu anna Muhammadan ‘abduhu wa rasooluhu (or anna Muhammadan
rasool-Allaah) [All compliments are due to Allaah, Peace be upon you, O
Prophet, and the mercy of Allaah, Peace be upon us, and on the righteous
slaves of Allaah. I bear witness that there is no god except Allaah, and I
bear witness that Muhammad is His slave and Messenger (or that Muhammad is
the Messenger of Allaah)].”

End quote. 

And Allaah knows best.