פירוש על עבודה זרה 43:2

The Talmud notes that there is an additional reason for why it is prohibited to rent a field to a Samaritan. This will give the Samaritan an opportunity to work the field on hol hamoed. Providing a person with an opportunity to transgress is considered placing a stumbling block before the bling. Thus there are really two reasons why one should not do this.