Qatadah narrated that a man who had killed another man was brought before Sayyiduna Umar bin al-Khattab (may Allah be pleased with him). The sons of the slain man came, and one of them had forgiven. Sayyiduna Umar (may Allah be pleased with him) asked Sayyiduna Ibn Mas'ud (may Allah be pleased with him), who was at his side: "What is your view?" Sayyiduna Ibn Mas'ud (may Allah be pleased with him) said: "In my view, he has been saved from being killed." The narrator said: So Sayyiduna Umar (may Allah be pleased with him) struck him on his shoulder and said: "He is a vessel filled with knowledge."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9700