The Messenger of Allah ﷺ said, "When you weigh, give generous measure."
قال رسول الله ﷺ: إذا وزنتم فأرجحوا.
No references are available.
Ibn Majah (2222), Abu Awana (3/255), and Qudai in Musnad Shihab (759) all narrated it from the hadith of Abdul-Samad, who said, "Shubah narrated to us, from Muharib bin Dithar, from Jabir bin Abdullah," and he mentioned it. Its chain of transmission is sahih.