SB 7.2.60

ataḥ śocata mā yūyaṁ
 paraṁ cātmānam eva vā
ka ātmā kaḥ paro vātra
 svīyaḥ pārakya eva vā
sva-parābhiniveśena
 vinājñānena dehinām
Synonyms: 
ataḥ — therefore; śocata — lament for; — do not; yūyam — all of you; param — another; ca — and; ātmānam — yourself; eva — certainly; — or; kaḥ — who; ātmā — self; kaḥ — who; paraḥ — other; — or; atra — in this material world; svīyaḥ — one’s own; pārakyaḥ — for others; eva — indeed; — or; sva-para-abhiniveśena — consisting of absorption in the bodily concept of oneself and others; vinā — besides; ajñānena — the lack of knowledge; dehinām — of all the embodied living entities.
Translation: 
Therefore none of you should be aggrieved for the loss of the body — whether your own or those of others. Only in ignorance does one make bodily distinctions, thinking “Who am I? Who are the others? What is mine? What is for others?”
Purport: 

In this material world, the conception of self-preservation is the first law of nature. According to this conception, one should be interested in his personal safety and should then consider society, friendship, love, nationality, community and so on, which have all developed because of the bodily conception of life and a lack of knowledge of the spirit soul. This is called ajñāna. As long as human society is in darkness and ignorance, men will continue to make huge arrangements in the bodily conception of life. This is described by Prahlāda Mahārāja as bharam. In the materialistic conception, modern civilization makes enormous arrangements for huge roads, houses, mills and factories, and this is man’s conception of the advancement of civilization. People do not know, however, that at any time they themselves may be kicked out of the scene and forced to accept bodies that have nothing to do with these enormous houses, palaces, roads and automobiles. Therefore when Arjuna was thinking in terms of his bodily relationships with his kinsmen, Kṛṣṇa immediately chastised him, saying, kutas tvā kaśmalam idaṁ viṣame samupasthitam anārya-juṣṭam: “This bodily conception of life is befitting the anāryas, the non-Āryans, who are not advanced in knowledge.” An Āryan civilization is a civilization advanced in spiritual knowledge. Not merely by stamping oneself an Āryan does one become an Āryan. To keep oneself in the deepest darkness concerning spiritual knowledge and at the same time claim to be an Āryan is a non-Āryan position. In this connection, Śrīla Madhvācārya quotes as follows from the Brahma-vaivarta Purāṇa:

ka ātmā kaḥ para iti dehādy-apekṣayā

na hi dehādir ātmā syān
 na ca śatrur udīritaḥ
ato daihika-vṛddhau vā
 kṣaye vā kiṁ prayojanam

yas tu deha-gato jīvaḥ
 sa hi nāśaṁ na gacchati
tataḥ śatru-vivṛddhau ca
 sva-nāśe śocanaṁ kutaḥ

dehādi-vyatiriktau tu
 jīveśau pratijānatā
ata ātma-vivṛddhis tu
 vāsudeve ratiḥ sthirā
śatru-nāśas tathājñāna-
 nāśo nānyaḥ kathañcana

The purport is that as long as we are in this human form of body, our duty is to understand the soul within the body. The body is not the self; we are different from the body, and therefore there is no question of friends, enemies or responsibilities in terms of the bodily conception of life. One should not be very anxious about the body’s changing from childhood to boyhood, from boyhood to old age and then to apparent annihilation. Rather, one should be very seriously concerned about the soul within the body and how to release the soul from the material clutches. The living entity within the body is never annihilated; therefore one should surely know that whether one has many friends or many enemies, his friends cannot help him, and his enemies cannot do him any harm. One should know that he is a spirit soul (ahaṁ brahmāsmi) and that the constitutional position of the soul is unaffected by the changes of the body. In all circumstances, everyone, as a spirit soul, must be a devotee of Lord Viṣṇu and should not be concerned with bodily relationships, whether with friends or with enemies. One should know that neither we ourselves nor our enemies in the bodily conception of life are ever killed.