The gemarah in 58b learns out this din of yemin l’mizrach (the l’mizrach is only agav orcha- mizrach is only possible by zevachim -Rashi) from a posuk in Divrei HaYomim.
I imagine that if you are going to turn it is better to turn right- to the side of chesed, than left -to din. But either way, Rami bar Yechezekel makes this lumid and the gemarah says that everyone has it.