BabylonianTalmud, Ta'anit 20a-b

Our Rabbis have taught: One should always be gentle as the reed and never unyielding as the cedar. Once R. Eleazar son of R. Simeon was coming from Migdal Gedor, from the house of his teacher, and he was riding leisurely on his donkey by the riverside and was feeling happy and elated because he had studied much Torah. There chanced to meet him an exceedingly ugly man who greeted him, ‘Peace be upon you, Sir’. He, however, did not return his salutation but instead said to him, ‘Reika (Worthless!), how ugly you are. Are all your fellow citizens as ugly as you are?’ The man replied: ‘I do not know, but go and tell the craftsman who made me, "How Ugly is the vessel which you have made".’ When R. Eleazar realized that he had done wrong he dismounted from the donkey and prostrated himself before the man and said to him, ‘I submit myself to you, forgive me’. The man replied: ‘I will not forgive you until you go to the craftsman who made me and say to him,"How ugly is the vessel which you have made".’ He [R. Eleazar] walked behind him until he reached his native city. When his fellow citizens came out to meet him greeting him with the words, ‘Peace be upon you O Teacher, O Master,’ the man asked them, ‘Whom are you addressing thus’? They replied, ‘The man who is walking behind you.’ Thereupon he exclaimed: ‘If this man is a teacher, may there not be any more like him in Israel’! The people then asked him: ‘Why’? He replied: ‘Such and such a thing has he done to me. They said to him: ‘Nevertheless, forgive him, for he is a man greatly learned in the Torah.’ The man replied: ‘For your sakes I will forgive him, but only on the condition that he does not act in the same manner in the future.’ Soon after this R. Eleazar son of R. Simeon entered [the Beit Hamidrash] and expounded thus, A man should always be gentle as the reed and let him never be unyielding as the cedar. And for this reason the reed merited that of it should be made a pen for the writing of the Law, Tefillin and Mezuzot. [Soncino translation]