Sunan at-Tirmithiy كتاب تفسير القرآن باب ومن سورة التوبة
Thawbān [al-Hāshimī] related, “We were on a journey with the Prophet, peace and blessings of God be upon him, when the verse: ‘…those who hoard gold and silver…’ (9 [at-Tawbah]: 34) was revealed [to him]. Some of his Companions commented, ‘This verse is about gold and silver ... if only we knew which type of wealth is considered the best so that we can [try to] acquire it!’ The Messenger of God, peace and blessings of God be upon him, said, ‘The best wealth is a tongue engaged in the remembrance of God, a grateful heart, and a believing wife who assists her husband in strengthening his faith.’” Click on ḥadīth to read more