What is the saying of the Qadariyyah, and how can they be refuted, especially those who link human will and power of concentration to the noble Hadith, "Supplicate to Allah while you are certain of the answer," so that they make certainty the influential factor rather than supplication itself?

The Qadariyyah are deniers of destiny, believing that Allah does not know things until after they occur. This is a misguided and blasphemous statement, for the truth is that Allah Almighty knows everything before its creation and has inscribed the destinies of all creatures. This has been indicated by Quranic verses and prophetic hadiths that affirm Allah's prior knowledge and effective will, such as His saying, "Indeed, We created all things with a [decreed] measure" (Quran 54:49) and "No disaster strikes upon the earth or among yourselves except that it is in a register before We bring it into being" (Quran 57:22). The Companions disavowed the statement of the Qadariyyah, such as Abdullah ibn Umar, who said: "If one of them had gold equal to Mount Uhud and spent it [in charity], Allah would not accept it from him until he believes in divine decree." The Ahl as-Sunnah wa al-Jama'ah (Sunnis) believe that humans have a choice and a will, which is the basis of accountability, and that Allah has affirmed a will for the servant, but it does not take effect except by His will. The servant is truly the doer of his actions and is therefore held accountable for them. The requirement of certainty for the acceptance of supplication is among the conditions for acceptance, and supplication is not useless. There is no similarity between the monotheist Muslim and the idol worshiper; appealing to destiny to justify sins is invalid, and the polytheist does that by his own choice.