Mistakes In Grammar

It has been mentioned:

ومر عمر بن الخطاب رضي الله عنه على قوم يسيئون الرمي، فقرعهم، فقالوا: إنا قوم ” متعلمين ” ، فأعرض مغضباً، وقال: والله لخطؤكم في لسانكم، أشد علي من خطئكم في رميكم

Omar Ibn al-Khattab passed by some people who were making mistakes in archery.
When he rebuked them, one of them said: “We are just learners” (but he made a mistake by saying muta’alimeen instead of muta’alimoon).
Omar turned away in anger and said: “Your tongue’s mistakes are more severe than your mistakes at archery!”

[“Mu’jam Al-Udaba”, 1].