Don't hand gold to a rotten fool; his temperament is out of balance.
Friendship is good only up to a point; beyond that it brings nothing but worry and heartache.
Explanation: The Persian uses crude, satirical idioms; I have rendered the intent in a plainer register while keeping the cautionary, mocking tone.
Original · Persian
شمارهٔ ۱۸
زر به خر کندهای نباید داد
که مزاجش نه معتدل باشد
دوستی تا به خایه نیک بود
ورنه تیمار و درد دل باشد