Ibn Battah records that Imām Ahmad – Allāh have mercy on him – said:

No man should appoint himself to issue verdicts (fatwa) until and unless he fulfills five characteristics:

• First, he should have a [firm and good] intention; for if he does not, he will have no light upon him, and nor will his words.
• Second, he should be forbearing, tranquil and serene.
• Third, he should be strong upon what he is involved in, strong in its knowledge.
• Fourth, he should have sufficient means (wealth), otherwise the people will chew him up.
• Fifth, he should know people and their ways.

Ibn Battah, Ibtāl Al-Hiyal p24.

After quoting this statement, and before his commentary on it, Ibn Al-Qayyim states:

This is one of the proofs of the eminence of Imām Ahmad and his lofty status in knowledge and insight; for these five are the pillars of fatwā, and to the extent that there is deficiency in any of them, to that extent faults will appear in the mufti.

I’lām Al-Muwaqi’īn, 6:106