Musnad Ahmad 132:25

Yahya ibn Ghaylan narrated to us, Rashdin narrated to us, from Zabban, from Sahl, from his father, from the Prophet (peace and blessings of Allah be upon him), that a woman came to him and said: "O Messenger of Allah, my husband has gone out as a warrior (ghazi), and I used to follow his prayer when he prayed, and all of his actions. So inform me of a deed that will make me reach his deed until he returns." He said to her: "Are you able to stand and not sit, and fast and not break your fast, and remember Allah, Blessed and Exalted is He, and not grow weary until he returns?" She said: "I cannot endure that, O Messenger of Allah." He said: "By the One in Whose hand is my soul, if you were to be capable of it, you would not reach one-tenth of his deed until he returns."