“Whoever guards Allah’s limits in his youth and strength, Allah will guard him in his old age and weakness.”

Ibn Rajab (736–795 AH / 1335–1393 CE) writes this in his commentary on the hadith “be mindful of Allah and He will protect you,” and tells the story that goes with it: a scholar past a hundred years old, still strong and sharp, once leapt up so vigorously that people rebuked him, and he said, “These are limbs we guarded from sin when we were young, so Allah has guarded them for us now that we are old.”