One day Lord Hanuman was sitting under the trees and was praying Lord Rama. Lord Shani Dev appeared and said to Lord Hanuman that I am the powerful Lord Shani Dev. I heard you are also powerful, so I want to test your strength. Open your eyes and prove that to me.
In reply to Lord Shani Dev, Lord Hanuman opened his eyes and said that I request you not to disturb me in my prayer and leave me alone. But Shanidev insisted again and again. Seeing this Lord Hanuman stretched out his tail and started binding it around Shani. Lord Shani Dev tried to free himself but could not. Lord Hanuman moved his tail up & down hitting him against the stone and Lord Shani Dev started bleeding.
When the pain was unbearable and on the repeated request of Lord Shani Dev, Lord Hanuman released him, and then he asked Lord Hanuman for some oil to reduce his pain.
Since then oil is offered to Lord Shani Dev for soothing his pain. He feels satisfied and blesses the Devotee of all Lord Hanuman who will offer Oil to Lord Shani dev. . . . Our Beloved Guru Rajneesh Rishi Describes.