Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) said: I said: O Messenger of Allah, tell me of a deed that will admit me into Paradise. He (peace and blessings be upon him) said: "If you wish, I will tell you which of these is the head, which is the pillar, and what is the peak of the hump." Then he said: "The head of these matters is Islam; whoever accepts Islam is safe. Their pillar is prayer, and the peak of the hump is jihad." Then he narrated the hadith.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 17797