Musnad Ahmad 456:17

Rawh narrated to us, he said: Husayn al-Mu'allim narrated to us, he said: Yahya ibn Abi Kathir narrated to us, from Abu Salamah, from Busr ibn Sa'id, from Zayd ibn Khalid al-Juhani, that the Prophet of Allah, peace and blessings of Allah be upon him, said: "Whoever equips a warrior in the way of Allah, then he has indeed fought. And whoever looks after the family of a warrior in a good manner, then he has indeed fought."