Mishnah for Bekhorot 60:22

One who takes upon himself to become a “chaver” may not sell to an am haaretz either moist or dry [produce], nor may he buy from him moist [produce], nor may he be the guest of an am haaretz, nor may he host an am haaretz as a guest while [the am haaretz] is wearing his own garment. Rabbi Judah says: he may not also raise small animals, nor may make a lot of vows or merriment, nor may he defile himself by contact with the dead. Rather he should be an attendant at the house of study. They said to him: these [requirements] do not come within the general rule [of being a chaver].