Ат-Тин 95:6

إِلَّا الَّذِينَ آمَنُوا وَعَمِلُوا الصَّالِحَاتِ فَلَهُمْ أَجْرٌ غَيْرُ‌ مَمْنُونٍ ‌ (except those who believed and did righteous deeds, because for them there is a reward never ending....95:6). The foregoing interpretation of the preceding verse should not be misunderstood. The exceptive sentence does not mean that the believers will not attain to decrepit old age. It would not be correct to exclude the believers from this, because some of them are also overcome by the senility of old age. The sense, however, is that they do not suffer a big harm due to their physical or mental deterioration in old age. Only those will suffer from it who spent their entire energy on improving their physical condition that has now ended. They shall have no portion of it in the Hereafter. The righteous believers will have an unfailing reward. This verse makes it clear that even after reaching old age, a believer never becomes useless. Even in decrepitude he can accumulate rewards - comfort and high positions - for the Hereafter that are eternal. During the period of senility when he is unable to do righteous deeds, the good deeds will be recorded in his Record Book which he used to do in good health. Sayyidna Anas ؓ narrates that the Holy Prophet ﷺ said that when a Muslim falls ill Allah instructs the recording angels to record the good deeds he used to perform in good health. [ Al-Baghawi transmitted it in Sharh-us-Sunnah from Abu Musa, and Bukhari has reported the same rewards for a traveller and a person suffering from a disease.) Here instead of mentioning the rewards and blessings of Paradise for the righteous believers, the verse reads: لَهُمْ أَجْرٌ‌ غَيْرُ‌ مَمْنُونٍ (for them there is a reward never ending.) This could signify that their reward starts in this mortal world [ and continues in the Hereafter eternally ]. Allah gathers around them in their decrepit old age such sincere companions who benefit from them spiritually until the last moment of their life. They serve them in every possible way. The righteous servants of Allah in decrepitude are productive while generally the senile and people in bad health are thought to be unproductive.

Some commentators say that the statement - رَ‌دَدْنَاهُ أَسْفَلَ سَافِلِينَ (We turned him into the lowest of the low) does not refer to human beings in general. It refers specifically to unbelievers who destroyed the God-given best composition, human perfection, honour and intellect by pursuing physical pleasures. As a result of their ingratitude, they will be turned into the lowest of the low. In this interpretation, the exception - إِلَّا الَّذِينَ آمَنُوا (except those who believed and did righteous deeds, because for them there is a reward never ending) will carry its basic interpretation, in that they will not be turned into the lowest of the low. For those who believed and did righteous deeds, there is a reward that is unending. [ Thus in al-Mazhari ].