Yam Has No Power to Punish Vaishnav
If anybody wants that he should not face Yam Raaj, he must worship Shree Hari or love Hari's things -Hari things means - Aamalaa, Tulasee, Vaishaakh and Kaarttik Maas, Ekaadashee, reading Bhaagvat Puraan, reciting Vishnu Sahastra Naam etc. All who love these things, eat Aamalaa, water Tulasee plant, do Snaan and fast in Vaishaakh Maas, keep Ekaadashee fast, recite Bhaagvat or Vishnu Sahastra Naam or Tulasee Stotra, cow donation (as cow is another form of Vishnu), etc, Yam Raaj has no control on those people because they come under the category of Vishnu Bhakt (devotees).
This he has cleared several times himself to his Doot (messengers). In Bhaagvat Puraan, in its Mahaatmya (Glory), in its 6th chapter, comes a reference for this that - "Seeing the Paash in his Doot's hands, Yam Raaj says to them - "Do not go near where Vishnu's Kathaa is going on, because I can punish all other people but I do not have power to punish Hari's devotees - Vaishnav." and there are some stories too in this regard. Here are given some stories ---
Vishnu's Name and Things
(1) In Padm Puraan, 4/21, Yam Raaj tells a story of King Maheerath who being a Vishnu Bhakt relieved people suffering in Narak (Hell) just by passing nearby the Hell.
(2) A story comes in Vishnu Puraan, 3/3, that once Yam Doot went to bring somebody from the Earth at his death. That man was a great sinner so Yam's Doot got ready to take his soul away, but suddenly he called Vishnu's name at the time of his death, and as Vishnu's Paarshad were roaming around, they heard Vishnu's name and they came rushing to him. They found that Yam's Doot were ready to take his soul. They fought with them and got succeeded in taking that man's soul to Vaikunth Lok.
Tolerating the insult at Vishnu's Paarshad, Yam's Doot came to Yam Raaj and complained about the incident. So this chapter is about Yam Raaj explaining them that why were they defeated at the hands of Vishnu's Paarshad? And who are those people upon whom he does not have any control - "I cannot take those people who worship Vishnu, who take name of Vishnu and who call Vishnu at the time of their death, because Vishnu is respectable for me, because He is my Creator. I cannot disregard Him."
(3) Who does not know the story of Ajaamil. It comes in Bhaagvat Puraan, 6/1. Ajaamil was a Braahman but since he lived with a maidservant his all Braahman like qualities were gone. He had 10 sons among whom he named his youngest son as Naaraayan. He loved him very much. He lived for 88 years. When he was about to die, he started calling "Naaraayan, Naaraayan". Since he was a great sinner Yam's Doot were present there to take his soul to Yam Raaj, but when he was dying he was calling "Naaraayan, Naaraayan", and Naaraayan is Vishnu's one name, so Vishnu's Paarshad came immediately and wanted to take his soul to Vaikunth Dhaam. Yam's Paarshad argued them over this matter as how could they take his soul because he was great sinner and they had the first right over his soul, but Vishnu's Paarshad convinced them since he was taking Vishnu's name at the time of his death, that is why they were the right people to take Ajaamil's soul and they took it to Vaikunth Dhaam. Such is the power of Vishnu's name. That discussion is given here in this chapter.
(4) One story comes in Padm Puraan, 1/31 in which Yam's Doot could not take the soul of even a Chaandaal (the lowest level of people in Indian society) because he had eaten Aamalaa fruit.
(5) In Padm Puraan, 1/31 Yam Raaj sent his Doot to bring one Mudgal's soul, but his Doot brought Muni Mudgal's soul. Seeing Muni Mudgal Yam Raaj scolded his Doot and asked them to bring the Kshatriya Mudgal's soul, not Muni's Mudgal's soul. Even Mudgal Rishi tells them that whoever has eaten Aamalaa fruit does not go to Hell.
Release From Pret Yoni
Pret Yoni is the result of many sins. It is also a kind of Narak. Vishnu's name has an effective effect on getting free from Pret Yoni. There are some incidents showing this in several Puraan. Even the name of Vishnu and using of Vishnu's things have also freed people from their Pret Yoni.
(1) One main story of such subject is about Dhundhukaaree comes in Bhaagvat Puraan while describing its Mahaatmya (Glory), in its 5th chapter, Gokarn Jee uplifts his brother Dhundhukaaree from Pret Yoni by telling Bhaagvat's Kathaa to him.
(2) In Padm Puraan, 4/20 gives a story of a Braahman, Muni Sharmaa and five Pret, in the dialog form of Raajaa Ambareesh and Naarad Jee. It is also related to Vaishaakh Maas importance with regard to upliftment from Pret Yoni.
(3) In Padm Puraan, 4/21, Yam Raaj also tells a story of Dhan Sharmaa. He meets three Pret and he gives them relief just by taking the name of Vishnu. Since Vaishaakh Maas is Vishnu's month, Dhan Sharmaa did Snaan in that month and freed them from Pret Yoni.
Thus they all are examples showing of the incapability of Yam Raaj's control over Vishnu Bhakt. That is why one must worship Vishnu or love His things (as given above) to save oneself from Hell and Yam Raaj.