You have also asked, what is sincerity to God (Ikhlas)? You should know that Ikhlas is that, all of your deeds should be exclusively for the sake of Allah [and His pleasure]. Whatever you do, it should not be for show off (ostentation/Riya). When you do good deeds, your heart should not be inclined towards people [to impress them and to gain their praise]. Your heart should not be pleased at the admirations (praises) of the people, nor should [your heart] be grieved at their complaints [or criticisms]. You should know that Riya (show off/ostentation) is born out of people’s praises and honors and the cure of [the spiritual disease of] Riya (show off/ostentation) is that you consider the entire universe subservient to the Power (Control) of Allah, the Exalted, and consider all creations [of Allah] equivalent (similar) to the pebbles and stones, you should understand this that stones do not have the power to bring you either grief or comfort. If you consider all creations like this (i.e. like stones and pebbles) then you will get rid of Riya (show off/ostentation). Until you have this belief that the [mortal] creations have power to bring you grief and comfort, then Riya (show off/ostentation) will never get out of your heart.