In the Name of Allaah, Ar-Rahmaan, Ar-Raheem...
'Uthmaan ibn Khur-raazaad [d.282], one of Imaam An-Nasaa'ee's shuyookh, said:
"The companion of hadeeth is in need of five things, and if he misses any one of them, then it is a deficiency. He needs:
 A good intellect;
 (Uprightness in the) Deen;
 Expertise in the field;
 While being known to fulfill trusts."
Ath-Thahabee mentioned this in Siyar (13/380), and then commented:
"I say: Trustworthiness is a part of the Deen (ie. #5 is included in #2), and precision is included in expertise (ie. #3 is included in #4), so what the haafith (one who memorizes hadeeth) needs is to be:
 A person of taqwaa;
 Knowledgeable of 'Arabic grammar and language;
 Pure and shy;
It will suffice him that he copies with his hand 200 volumes of books, owns 500 volumes of widely respected books, and does not tire from seeking knowledge until his death, all of this with a pure intention and humbleness. Otherwise, then he shouldn't waste his time (by trying to be a haafith)."
Translated by Abul-'Abbaas Moosaa Richardson