The Prophet صلى الله عليه وسلم said:
إنَّ الكافِرَ إذا عَمِلَ حَسَنَةً أُطْعِمَ بها طُعمةً في الدنيا، وَأَمّا المؤمن فَإِنَّ الله يَدَّخرُ له حَسَناته في الآخرة وَيُعقِبُهُ رزْقاً في الدينا عَلى طاعَتِهِ
Indeed when a non-Muslim does a good deed he is rewarded for it in the worldly life. As for the Muslim, Allāh will store his good deeds in the hereafter and subsequently give him provisions in the worldly life for his acts of obedience.” (Muslim)
Shaykh Zayd رحمه الله :
I say: Know - O believer - that Allāh is All Wise in His rewarding; Just in all affairs related to His creation. He rewards every doer for his actions, even the non-Muslim. When the non-Muslim does actions of good Allah rewards him for his good in this life with wealth, children, good health, safety and other than that from food, drink, transportation and various blessings of the world. This is his reward only in this world. When he comes on the Day of Judgement he will not have any good deed that He is rewarded for. This is because he didn’t come with the foundation in which deeds are accepted and this is the Tawheed of Allah. He only comes with shirk (ascribing partners with Allah) either being a pagan that worships idols or either a Jew that worships three or also a Christian from the people of the trinity or a hypocrite with major hypocrisy who is deceptive with his outward actions. All of these people will never have good deeds on the Day of Judgement. They will be for the fire and what an evil end. As for the believer, Allāh will give them success to good deeds and store those deeds for them on the Day of judgment and will also multiply them by ten fold. As Allah says:
Whoever comes with a good deed he will have ten fold of its kind and whoever comes with a evil deed, he will not be recompensed excepted with its like and they will not be wronged”
Rather Allah will multiply their good more than that. As Allah says:
Who is it that would loan Allah a goodly loan so He will multiply it for him and he will have a noble reward.
The word ‘reward’ in the verse came in a general form which indicates a lot and a great amount. Also it was reported that the Prophet صلى الله عليه وسلم said:
Indeed Allah fosters the charity of his servant just as one of you fosters his young horse.
So the small amount is like a great mountain, as a mercy to the people of faith and goodness towards them because they have come with the means of (receiving) mercy which is faith in Allah, His messengers, His books, His angels, the pre-decree; the good of it and the evil of it and in the Day of Judgement. They make permissible what is permissible, they make unlawful what is unlawful and complying with the commands, avoiding the prohibitions; out of obedience to Allah and fearing the punishment of Allah. So Allāh will have mercy upon them in this life, the grave and the hereafter. And he will increase their good deeds and their sustenance will come to them in this life which He has written for them. So Allāh will combine for them the reward of the worldly life and reward of the hereafter and this is from the virtue of Allah upon them.”
Translated by Abu Anas Atif Hasan
Source: at-Ta’aleeqaat al-Hisaan ‘ala Usul al-Imaan by Imam Muhammad ibn Abdul-Wahhab explained by Shaykh Zayd al-Madhkhali pg. 34