Every Saturday past midnight a special prayer (puja) is performed at the temple of Hanuman Ji Maharaj to pacify the effects of Shanidev (Saturn). According to Hindu scriptures, when Hanuman Ji was returning back to Sri Ram after setting Lanka ablaze, then shanidev who was a prisoner of Ravana requested Hanuman Ji to set him free.
Hanuman Ji told him that his wish would be granted on the condition that Shanidev would then never again trouble his devotees and let them live their life peacefully. Shanidev agreed however he asked for one day in the week (Saturday) during which his powers and its effect would still work.
Hanuman Ji obliged and set him free. Since that day on every Saturday past midnight, an offering is made to Hanuman Ji by dressing him in new clothes.
This prayer (aarti) has special significance for people who are suffering from incurable diseases as well as for granting their wishes.