Zayd bin Wahb (may Allah have mercy on him) said: We were sitting with Sayyiduna Umar (may Allah be pleased with him) when Sayyiduna Abdullah (bin Mas'ud) (may Allah be pleased with him) came; he was so short that he seemed level with those who were sitting. Sayyiduna Umar (may Allah be pleased with him) laughed when he saw him. Then he (Ibn Mas'ud), standing over him, began talking with Sayyiduna Umar (may Allah be pleased with him) and making him laugh. Then he turned away, and Sayyiduna Umar (may Allah be pleased with him) kept watching him until he was out of sight, and then said: "A small vessel filled with understanding of the religion (fiqh)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 8445