Musnad Ahmad 31:774

Husayn narrated to us, Ibn ‘Ayyash—meaning Isma‘il—narrated to us, from al-Hajjaj ibn Marwan al-Kala‘i and ‘Aqil ibn Mudrik al-Sulami, from Abu Sa‘id al-Khudri, that a man came to him and said: "Advise me." He said: "You have asked about what I asked the Messenger of Allah, peace and blessings of Allah be upon him, before you. I advise you to fear Allah, for it is the head of everything. And upon you is Jihad, for it is the monasticism of Islam. And upon you is the remembrance of Allah and the recitation of the Quran, for it is your spirit in the heaven and your mention on the earth."