Is there harm to worship or sin upon its doer if the abundance of it is for the sake of worldly reward?

It does not harm a servant if they do not increase in acts of obedience for which no worldly reward has been mentioned, nor is there sin in reducing them as long as they are not obligatory. One should not be negligent in obedience due to the absence of a textual mention of a worldly reward, for righteous deeds are a cause for Allah's love and pleasure. And whoever Allah loves, He fulfills their desires and sets right their worldly and otherworldly affairs. Allah Almighty said: "Indeed, those who have believed and done righteous deeds - the Most Merciful will appoint for them affection." (Quran 19:96) And the Prophet, peace and blessings be upon him, said in what Al-Bukhari narrated from Abu Hurairah: "My servant continues to draw near to Me with supererogatory deeds until I love him, and when I love him, I am his hearing with which he hears, and his sight with which he sees..."