ʿUthmān ibn Khur-rāzād [d.282], one of Imām Al-Nasāʿī’s shuyūkh, said:

“The companion of ḥadīth is in need of five things, and if he misses any one of them, then it is a deficiency. He needs:

1. A good intellect;
2. (Uprightness in the) Dīn;
3. Precision;
4. Expertise in the field;
5. While being known to fulfill trusts.”

Al-Thahabī mentioned this in Siyar (13/380), and then commented:

“I say: Trustworthiness is a part of the Dīn (ie. #5 is included in #2), and precision is included in expertise (ie. #3 is included in #4), so what the hāfith (one who memorizes ḥadīth) needs is to be:

1. A person of taqwá;
2. Intelligent;
3. Knowledgeable of Arabic grammar and language;
4. Pure and shy;
5. Salafī.

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 pure intention and humbleness. Otherwise, then he shouldn’t waste his time (by trying to be a hāfith).”

Source: You need to be a SALAFĪ if you want to memorize hadīth! – Beautiful words from Imām Al-Thahabī
Translated by: Abū al-ʿAbbās Mūsá Richardson