The Quran

105

وَقُلِ اعمَلوا فَسَيَرَى اللَّهُ عَمَلَكُم وَرَسولُهُ وَالمُؤمِنونَ ۖ وَسَتُرَدّونَ إِلىٰ عالِمِ الغَيبِ وَالشَّهادَةِ فَيُنَبِّئُكُم بِما كُنتُم تَعمَلونَ

Muhammad Asad

And say [unto them, O Prophet]: "Act!¹ And God will behold your deeds, and [so will] His Apostle, and the believers: and [in the end] you will be brought before Him who knows all that is beyond the reach of a created being's perception as well as all that can be witnessed by a creature's senses or mind² - and then He will make you understand what you have been doing."

This connects with the injunction in verse 103 above, "accept that [part] of their possessions which is offered for the sake of God,... and pray for them". The stress on action as an integral part of faith is of fundamental importance in the ethics of the Qur'an: cf. the frequent juxtaposition of the concepts of "believing" and "doing good works", and the condemnation of all "who, while believing, wrought no good works" (see 6:158 and the corresponding note 160).
See Sarah 6, note 65.