What is the ruling regarding a scholar who shouts at a questioner, or embarrasses him, or speaks harshly to him?

A scholar should emulate Prophet Muhammad in teaching, being lenient, gentle, soft, and merciful with the student, so as not to alienate them. This is in accordance with the Almighty's saying: "It is by a mercy from Allah that you were lenient with them. And had you been rude [in speech] and harsh in heart, they would have disbanded from about you." In contrast, the student should be patient with their teacher's occasional harshness and severity, and should not abandon learning, and should offer sincere advice to their teacher.