Dogen instructed,

There is an old saying which goes, “Although the power of a wise man exceeds that of an ox, he does not fight with the ox.

Now, students, even if you think that your wisdom and knowledge is superior to others, you should not be fond of arguing with them. Moreover, you should not abuse others with violent words, or glare at others angrily. Despite having been given great wealth and receiving the favors of some person, people in this age would definitely have negative feelings if the donor were to display anger and slander them with harsh words. 

Once, Zen Master Shinjo told his students, 

In former times, I practiced together with Seppo. Once Seppo was discussing the dharma loudly with another student in the monk’s dormitory. Eventually, they began to argue using harsh words, and in the end, wound up quarreling with each other. After the argument was over, Seppo said to me, “You and I are close friends practicing together with one mind. Our friendship is not shallow. Why didn’t you help me when I was arguing with that man?” At the time, I could do nothing but feel small folding my hands and bowing my head.  

Later, Seppo became an eminent master, and I too, am now an abbot. What I thought at the time was that Seppo’s discussion of the dharma was ultimately meaningless. Needless to say, quarreling was wrong. Since I thought it was useless to fight, I kept silent.

Students of the Way, you also should consider this thoroughly. As long as you aspire to make diligent effort in learning the Way, you must be begrudging with your time. When do you have time to argue with others? Ultimately, it brings about no benefit to you or to others. This is so even in the case of arguing about the dharma, much more about worldly affairs. Even though the power of a wise man is stronger than that of an ox, he does not fight with the ox. Even if you think that you understand the dharma more deeply than others, do not argue, criticize, or try to defeat them.

“If there is a sincere student who asks you about the dharma, you should not begrudge telling him about it. You should explain it to him. However, even in such a case, before responding wait until you have been asked three times. Neither speaks too much nor talks about meaningless matters.” 

After reading these words of Shinjo, I thought that I myself had this fault, and that he was admonishing me. I have subsequently never argued about the dharma with others.