Musnad Abu Ya'la al-Mawsili 105:41

Surayj ibn Yunus narrated to us, Abd al-Rahman ibn Abd al-Malik ibn Abjar narrated to us, from his father, from Wasil ibn Hayyan, who said: Abu Wa'il said: Ammar ibn Yasir delivered a sermon to us, and he was concise and eloquent. When he descended, we said: "O Abu al-Yaqzan, you were indeed eloquent and concise; if only you had breathed (i.e., spoken at greater length)." He said: "I heard the Messenger of Allah (ﷺ) say: 'Verily, the length of a man's prayer and the shortness of his sermon are a sign of his understanding (fiqh). So lengthen the prayer and shorten the sermons, for indeed, some eloquence is magic.'"