Abdullah bin Awn (may Allah have mercy on him) wrote to Nafi' (may Allah have mercy on him) asking why Sayyiduna Ibn Umar (may Allah be pleased with them both) did not go out on the military expeditions. He wrote in reply that he used to send his son out on campaigns and provide riding mounts (for the fighters), and that nothing kept him back from fighting except the trusts left by Sayyiduna Umar (may Allah be pleased with him) and young children; and Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) regarded jihad in the way of Allah as superior to all other deeds after the obligatory prayer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 17945