Lengthening the hair on the head for a man: is it part of the Sunnah or not?

Question:
Honorable Shaykh, may Allah grant you success. Is lengthening the hair on the head for a man part of the Sunnah or not? And is it established that Imam Ahmad (may Allah have mercy on him) said, "If we were able to maintain it, we would leave it [long]"?

Answer:
Whoever lengthens his hair in the manner reported from the Prophet (peace and blessings be upon him), if he knows the Sunnah, and lengthens it based on the Sunnah of the Messenger and acts in it as the Messenger acted, then this is Sunnah. As for whoever lengthens it imitating the disbelievers, imitating the wicked, and imitating the innovators, this is not considered Sunnah. The criterion is the manner of the action. The one who knows the Sunnah of the Messenger and applies it, this is Sunnah. As for the one who does not know the Sunnah of the Messenger, but only sees that people have hair and long heads, and does not distinguish between the Sunnah and custom, this is not, yes.