Differences between Recomended andObligatory Caution

11 - Recomended caution is always accompanied by a Fatwa, in addition to a Fatwa, there is caution which is explained bythe Mujtahid and the follower can act according to the Fatwa or to caution and cannot refer to another Mujtahid. For example:
"If he/she says that, if an impure (Najis) vesselis washed once with Kurr water (a minimum of one Kurr of water is approximatly 388 liters) it becomes pure (PAK) although as a precaution it should be washed three times."

Obligatory caution is not accompanied by a Fatwa and the follower acts according to caution and can refer to another Mujtahid¨s Fatwa. For example:
It is obligatory that a human does not prostrate ( to Allah ) on the leaf of a grape tree, if it is fresh.