Sayyiduna Abu Hurayrah (may Allah be pleased with him) narrated that the Companions said: "O Messenger of Allah (peace and blessings be upon him)! What is equal to jihad in the path of Allah?" He (peace and blessings be upon him) said: "You are not able to do it." We said: "Certainly we are!" He (peace and blessings be upon him) said: "You are not able to do it." The narrator said: I do not know whether on the third or the fourth time he (peace and blessings be upon him) said: "The one who strives in the path of Allah is like one who fasts continuously and constantly stands (in prayer) reciting the Qur'an, never slackening in fasting or prayer, until the fighter in the path of Allah returns home."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18489