“Love thy neighbour as thyself” appears in Leviticus 19 and is quoted by Jesus in Mark 12 and by Paul in Romans 13.
In Mark 12:31:
31 And the second is like, namely this, Thou shalt love thy neighbour as thyself. There is none other commandment greater than these.
In Leviticus 19:18:
18 Thou shalt not avenge, nor bear any grudge against the children of thy people, but thou shalt love thy neighbour as thyself: I am the LORD.
In Romans 13:9-10:
9 For this, Thou shalt not commit adultery, Thou shalt not kill, Thou shalt not steal, Thou shalt not bear false witness, Thou shalt not covet; and if there be any other commandment, it is briefly comprehended in this saying, namely, Thou shalt love thy neighbour as thyself. 10 Love worketh no ill to his neighbour: therefore love is the fulfilling of the law.