What is the evidence for the prohibition of letting the beard grow longer than a fist's length?

The questioner : Since you said that letting the beard hang down is like letting the garment hang below the ankles, what is the evidence for the prohibition of letting the beard hang down more than a fist's length?

The Shaykh : The evidence.

The questioner: Yes.

The Shaykh : The practice of the Salaf: Do you cite the practice of the Salaf as evidence?

The questioner : Yes, I cite it as evidence. Yes.

The Shaykh : Yes, and all good is in following the Salaf.

The questioner: Yes.

The Shaykh : And all evil is in the innovation of the Khalaf.

The questioner: Yes.

The Shaykh : Yes, and the Salaf did not let their beards grow long, no matter how long they grew; rather, they only took what exceeded a fist's length.
The student : Is this evidence for the prohibition?

The Shaykh : No, because it is the opposite. Letting the beard grow requires letting it grow completely. So long as this letting it grow was not practiced by the Salaf in its absolute form, we must follow their example.
The student : Well, what is the saying regarding the statement of the Messenger of Allah (peace and blessings be upon him): , ?

The Shaykh : May Allah guide you. What is the difference between what you mentioned and what I mentioned?
The student : I mean, this is a command to let the beard grow.

The Shaykh : May Allah guide you. Do not repeat your previous story to us. What is the difference between "let it hang down" and "let it grow"?
The student : "Let it hang down" involves the process of letting it hang down and lengthening it.

The Shaykh : And "let it grow" involves the process of letting it grow and lengthening it.
The student : So it is left.

The Shaykh : And letting it grow is likewise.
The student: Yes.