It is a popular fast, and is dedicated Mahavir Hanuman, who rendered great service to Lord Rama. On this day strict fast is kept, and Hanumanji is worshipped with sweets and fruits. The story of Mangalvar should be heard or read and Hanuman Chalisa is read and recited. From Mangalvar vrat, flows success, happiness, strength, both physical and moral, and quick recovery from illness. It also helps in overcoming the enemies.
Once there lived a Brahman couple. They were issueless. So their life was very unhappy. The Brahman went to the jungles to appease Lord Hanuman. He would pray for a child in his prayers. His wife used to observe fasts on Tuesdays to placate the Lord. She used to take her food on Mondays only after offering Prasad to Lord Hanuman. Once she observed some special fast for the whole day. So she could not offer Prasad to Hanuman. She was very sorry for it and felt guilty. She decided to observe a fast till the coming Tuesday.
She said to herself that she would take her meals only after offering Prasad to Hanuman. She became weak and fragile and even fainted due to the long fast. Hanuman took pity on her and appeared before her in the guise of a child. Hanuman said, I bless you with a beautiful son. He will always serve you, day and night. He then disappeared after blessing the lady.
Fortunately, the lady got a beautiful son. She named him Mangal. The Brahman returned home after some months. He saw a handsome child playing in his courtyard. He became suspicious and said to his wife, Whose child Is this? Have you indulged in adultery? The woman said politely, My dear husband, I am a chaste lady. I used to observe Tuesday fast in your absence to please Lord Hanuman. He has blessed me with this child. Please believe me.
The Brahman kept mum but deep in his heart, doubts began to curl up every moment. The lady was helpless. One day the Brahman was going to take his bath at some nearby well. The lady told him, Please take Mangal along with you. He is quite grown-up. He will fetch water for your bath. He will also rub your back.
The Brahman agreed and took the boy along with him. He thought it would be a good occasion to push him into the well and to get-rid of a sinful child for good. As the boy was to fetch water, the Brahman pushed the boy into the well and returned home. To her great surprise, the woman noticed that the Brahman did not have wet dhoti on his shoulders. She said, Have you taken your bath? The Brahman said, Yes.
The lady said, Please give me your wet dhoti to enable me to spread it on the string. The Brahman was nonplussed. He had guilty conscience. He murmured some words and tried to leave the house. The wife said, Where is my Mangal? Where is my Mangal? O! Mangal, appear before my eyes if I am a cheste lady and you are my true son.
To the great surprise of both the wife and the husband, Mangal appeared at the door. He embraced his mother and touched his fathers feet. That might Lord Hanuman appeared before the Brahman in his dreams and said, O! poor creature, I blessed you with a son, and you suspect your wife of adultery. You must feel sorry for it.
The Brahman realized his mistake. His wife regularly observed fasts on Tuesdays. Thereafter they led a happy life. It is said that whosoever reads or listens to this story and keeps regular fasts Lord Hanuman protects him from air evils and bestows all happiness.