Srimad Bhagavatam Canto 06, Chapter 01, Text 31

SB 6.1.31

vikarsato ’ntar hrdayad
 dasi-patim ajamilam
yama-presyan visnuduta
 varayam asur ojasa
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
The order carriers of Yamaraja were snatching the soul from the core of the heart of Ajamila, the husband of the prostitute, but with resounding voices the messengers of Lord Visnu, the Visnudutas, forbade them to do so.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
A Vaisnava, one who has surrendered to the lotus feet of Lord Visnu, is always protected by Lord Visnu’s order carriers. Because Ajamila had chanted the holy name of Narayana, the Visnudutas not only immediately arrived on the spot but also at once ordered the Yamadutas not to touch him. By speaking with resounding voices, the Visnudutas threatened to punish the Yamadutas if they continued trying to snatch Ajamila’s soul from his heart. The order carriers of Yamaraja have jurisdiction over all sinful living entities, but the messengers of Lord Visnu, the Visnudutas, are capable of punishing anyone, including Yamaraja, if he wrongs a Vaisnava.
Materialistic scientists do not know where to find the soul within the body with their material instruments, but this verse clearly explains that the soul is within the core of the heart (hrdaya); it is from the heart that the Yamadutas were extracting the soul of Ajamila. Similarly, we learn that the Supersoul, Lord Visnu, is also situated within the heart (isvarah sarva-bhutanam hrd-dese ’rjuna tisthati). In the Upanisads it is said that the Supersoul and the individual soul are living in the same tree of the body as two friendly birds. The Supersoul is said to be friendly because the Supreme Personality of Godhead is so kind to the original soul that when the original soul transmigrates from one body to another, the Lord goes with him. Furthermore, according to the desire and karma of the individual soul, the Lord, through the agency of maya, creates another body for him.
The heart of the body is a mechanical arrangement. As the Lord says in Bhagavad-gita (18.61):
isvarah sarva-bhutanam
 hrd-dese ’rjuna tisthati
bhramayan sarva-bhutani
 yantrarudhani mayaya
“The Supreme Lord is situated in everyone’s heart, O Arjuna, and is directing the wanderings of all living entities, who are seated as on a machine, made of the material energy.” Yantra means a machine, such as an automobile. The driver of the machine of the body is the individual soul, who is also its director or proprietor, but the supreme proprietor is the Supreme Personality of Godhead. One’s body is created through the agency of maya (karmana daiva-netrena), and according to one’s activities in this life, another vehicle is created, again under the supervision of daivi maya (daivi hy esa guna-mayi mama maya duratyaya). At the appropriate time, one’s next body is immediately chosen, and both the individual soul and the Supersoul transfer to that particular bodily machine. This is the process of transmigration. During transmigration from one body to the next, the soul is taken away by the order carriers of Yamaraja and put into a particular type of hellish life (naraka) in order to become accustomed to the condition in which he will live in his next body.
Srimad Bhagavatam Canto 06, Chapter 01, Text 30
Srimad Bhagavatam Canto 06, Chapter 01, Text 32