In the Holy Qur'an

And verity in the remembrance of Allah do the hearts find rest (13:28)

In the Traditions

Imam Ali said, "I searched for wealth and I did not find it other than through contentment. Adhere to contentment and you will become rich."

Imam Al-Hadi said, "The thankful person prospers more as a result of his thanks than as a result of the bounty which incited the thanks, because bounties are sources of delight (in this world), whereas to thank brings bounties in this world and hereafter."