Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, said:

وَأَبْغِضْ بَغِيضَكَ هَوْنًا مَا عَسَى أَنْ يَكُونَ حَبِيبَكَ يَوْمًا مَا

Hate whom you hate mildly, for perhaps he will become your beloved someday.

Source: Sunan At-Tirmidhi 1997, Grade:Sahih