Musnad Ahmad 962:111

Hassan narrated to us, Ibn Lahi'ah narrated to us, from Khalid ibn Abi 'Imran, from Abu Umamah al-Bahili, from the Messenger of Allah, peace and blessings of Allah be upon him, that he said: "Four [types of people] whose rewards continue for them after death: one who guards the frontier in the way of Allah, one who performs a deed for whom the reward of what he did continues, a man who gives charity so its reward is for him as long as it continues, and a man who leaves behind a righteous child who prays for him." *** Harun ibn Ma'ruf narrated to us, Ibn Wahb narrated to us, 'Amr ibn al-Harith informed me, from Sulayman ibn 'Abd al-Rahman, from al-Qasim, the freed slave of 'Abd al-Rahman, from Abu Umamah, that he heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "Whoever believes in Allah and the Last Day, let him not wear silk or gold." Abu 'Abd al-Rahman 'Abdullah ibn Ahmad said: And I heard it myself from Harun ibn Ma'ruf.