In the Holy Qur'an

So that you may not grieve for what has escaped you, nor be exultant at what He has given you. (57:23)

In the Traditions

The Prophet said, "Contentment is a wealth that never dries up", and "Contentment is an inexhaustible treasure."

Imam Jafar said, "Be patient in what befalls you, for this indeed is one of the greatest tasks."