From Sahih Muslim (Hadith 2009):
Abu Wa'il reported:'Ammar delivered to us the sermon. It was short and eloquent. When he (, Ammir) descended (from the pulpit) we said to him: 0 Abd al-Yaqzn, you have delivered a short and eloquent sermon. Would that you had lengthened (the sermon). He said: I have heard the Messenger of Allah (ﷺ) as saying: The lengthening of prayer by a man and the shortness of the sermon is the sign of his understanding (of faith). So lengthen the prayer and shorten the sermon, for there is charm (in precise) expression
Reference: Muslim 2009