SB 10.45.42-44

tad-aṅga-prabhavaṁ śaṅkham
 ādāya ratham āgamat
tataḥ saṁyamanīṁ nāma
 yamasya dayitāṁ purīm
gatvā janārdanaḥ śaṅkhaṁ
 pradadhmau sa-halāyudhaḥ
śaṅkha-nirhrādam ākarṇya
 prajā-saṁyamano yamaḥ
tayoḥ saparyāṁ mahatīṁ
 cakre bhakty-upabṛṁhitām
uvācāvanataḥ kṛṣṇaṁ
 sarva-bhūtāśayālayam
līlā-manuṣyayor viṣṇo
 yuvayoḥ karavāma kim
Synonyms: 
tat — his (the demon’s); aṅga — from the body; prabhavam — grown; śaṅkham — the conchshell; ādāya — taking; ratham — to the chariot; āgamat — He returned; tataḥ — then; saṁyamanīm nāma — known as Saṁyamanī; yamasya — of Lord Yamarāja; dayitām — beloved; purīm — to the city; gatvā — going; jana-ardanaḥ — Lord Kṛṣṇa, the abode of all persons; śaṅkham — the conchshell; pradadhmau — blew loudly; sa — accompanied by; hala-āyudhaḥ — Lord Balarāma, whose weapon is a plow; śaṅkha — of the conchshell; nirhrādam — the resounding; ākarṇya — hearing; prajā — of those who take birth; saṁyamanaḥ — the restrainer; yamaḥ — Yamarāja; tayoḥ — of Them; saparyām — worship; mahatīm — elaborate; cakre — performed; bhakti — with devotion; upabṛṁhitām — overflowing; uvāca — he said; avanataḥ — bowing down humbly; kṛṣṇam — to Lord Kṛṣṇa; sarva — of all; bhūta — living beings; āśaya — the minds; ālayam — whose residence; līlā — as Your pastime; manuṣyayoḥ — appearing as human beings; viṣṇo — O Supreme Lord Viṣṇu; yuvayoḥ — for the two of You; karavāma — I should do; kim — what.
Translation: 
Lord Janārdana took the conchshell that had grown around the demon’s body and went back to the chariot. Then He proceeded to Saṁyamanī, the beloved capital of Yamarāja, the lord of death. Upon arriving there with Lord Balarāma, He loudly blew His conchshell, and Yamarāja, who keeps the conditioned souls in check, came as soon as he heard the resounding vibration. Yamarāja elaborately worshiped the two Lords with great devotion, and then he addressed Lord Kṛṣṇa, who lives in everyone’s heart: “O Supreme Lord Viṣṇu, what shall I do for You and Lord Balarāma, who are playing the part of ordinary humans?”
Purport: 

The conchshell the Lord took from Pañcajana, which is called Pāñcajanya, is the same one He sounded at the beginning of the Bhagavad-gītā. According to the ācāryas, Pañcajana had become a demon in a way similar to that of Jaya and Vijaya. In other words, though appearing in the form of a demon, he was actually a devotee of the Lord. The Skanda Purāṇa, Avanti-khaṇḍa, describes the wonderful things that happened when Lord Kṛṣṇa sounded His conchshell:

asipatra-vanaṁ nāma
 śīrṇa-patram ajāyata
rauravaṁ nāma narakam
 arauravam abhūt tada
abhairavaṁ bhairavākhyaṁ
 kumbhī-pākam apācakam

“The hell known as Asipatra-vana lost the sharp, swordlike leaves on its trees, and the hell named Raurava became free of its ruru beasts. The Bhairava hell lost its fearfulness, and all cooking stopped in the Kumbhīpāka hell.”

The Skanda Purāṇa further states:

pāpa-kṣayāt tataḥ sarve
vimuktā nārakā narāḥ
padam avyayam āsādya

“Their sinful reactions eradicated, all the inhabitants of hell attained liberation and approached the spiritual world.”