Is the unanswered prayer an indication of the non-acceptance of deeds, and does ill-fortune (nahs) have a basis in religion?

The response to a supplication is not always the attainment of what is requested. It may be stored for the supplicant in the hereafter, or an equivalent evil may be averted from them. The Prophet, peace and blessings be upon him, said: "No Muslim supplicates with a supplication in which there is no sin or severing of kinship, except that Allah grants them one of three things: either He hastens for them their supplication, or He stores it for them in the hereafter, or He averts from them an evil equivalent to it." The absolute non-response to a supplication does not mean that the supplicant's deed is not accepted; rather, it may be due to the absence of a condition for response or the presence of an impediment.