1 John 4:21

21Andκαὶthisταύτηνtheτὴνcommandmentἐντολὴνwe haveἔχομενfromἀπ’Himαὐτοῦ,thatἵναthe [one]ὁlovingἀγαπῶντὸνGodθεὸνshould loveἀγαπᾷalsoκαὶtheτὸνbrotherἀδελφὸνof himαὐτοῦ.

And this commandment we have from Him, that the one loving God should love his brother also.