SB 10.82.3-6

niḥkṣatriyāṁ mahīṁ kurvan
 rāmaḥ śastra-bhṛtāṁ varaḥ
nṛpāṇāṁ rudhiraugheṇa
 yatra cakre mahā-hradān
īje ca bhagavān rāmo
 yatrāspṛṣṭo ’pi karmaṇā
lokaṁ saṅgrāhayann īśo
 yathānyo ’ghāpanuttaye
mahatyāṁ tīrtha-yātrāyāṁ
 tatrāgan bhāratīḥ prajāḥ
vṛṣṇayaś ca tathākrūra-
 vasudevāhukādayaḥ
yayur bhārata tat kṣetraṁ
 svam aghaṁ kṣapayiṣṇavaḥ
gada-pradyumna-sāmbādyāḥ
 sucandra-śuka-sāraṇaiḥ
āste ’niruddho rakṣāyāṁ
 kṛtavarmā ca yūtha-paḥ
Word for word: 
niḥkṣatriyām — rid of kings; mahīm — the earth; kurvan — having made; rāmaḥ — Lord Paraśurāma; śastra — of weapons; bhṛtām — of the holders; varaḥ — the greatest; nṛpāṇām — of kings; rudhira — of the blood; oghena — with the floods; yatra — where; cakre — he made; mahā — great; hradān — lakes; īje — worshiped; ca — and; bhagavān — the Supreme Lord; rāmaḥ — Paraśurāma; yatra — where; aspṛṣṭaḥ — untouched; api — even though; karmaṇā — by material work and its reactions; lokam — the world in general; saṅgrāhayan — instructing; īśaḥ — the Lord; yathā — as if; anyaḥ — another person; agha — sins; apanuttaye — in order to dispel; mahatyām — mighty; tīrtha-yātrāyām — on the occasion of the holy pilgrimage; tatra — there; āgan — came; bhāratīḥ — of Bhārata-varṣa; prajāḥ — people; vṛṣṇayaḥ — members of the Vṛṣṇi clan; ca — and; tathā — also; akrūra-vasudeva-āhuka-ādayaḥ — Akrūra, Vasudeva, Āhuka (Ugrasena) and others; yayuḥ — went; bhārata — O descendant of Bharata (Parīkṣit); tat — that; kṣetram — to the holy place; svam — their own; agham — sins; kṣapayiṣṇavaḥ — desirous of eradicating; gada-pradyumna-sāmba-ādayaḥ — Gada, Pradyumna, Sāmba and others; sucandra-śuka-sāraṇaiḥ — with Sucandra, Śuka and Sāraṇa; āste — remained; aniruddhaḥ — Aniruddha; rakṣāyām — for guarding; kṛtavarmā — Kṛtavarmā; ca — and; yūtha-paḥ — leader of the army.
Translation: 
After ridding the earth of kings, Lord Paraśurāma, the foremost of warriors, created huge lakes from the kings’ blood at Samantaka-pañcaka. Although he is never tainted by karmic reactions, Lord Paraśurāma performed sacrifices there to instruct people in general; thus he acted like an ordinary person trying to free himself of sins. From all parts of Bhārata-varṣa a great number of people now came to that Samanta-pañcaka on pilgrimage. O descendant of Bharata, among those arriving at the holy place were many Vṛṣṇis, such as Gada, Pradyumna and Sāmba, hoping to be relieved of their sins; Akrūra, Vasudeva, Āhuka and other kings also went there. Aniruddha remained in Dvārakā with Sucandra, Śuka and Sāraṇa to guard the city, together with Kṛtavarmā, the commander of their armed forces.
Purport: 

According to Śrīla Viśvanātha Cakravartī, Śrī Kṛṣṇa’s grandson Aniruddha remained in Dvārakā to protect the city because He is originally Lord Viṣṇu’s manifestation as the guardian of the spiritual planet Śvetadvīpa.