Purity: Ruling on Purity of Objects After Absence from Sight (Rule of Ghaybah)
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 220
If the body, clothing, or something else like a utensil or carpet becomes impure, and if it is in the possession of a Muslim who is bāligh – or a non-bāligh mumayyiz child who is able to discern between what is pure and what is impure – and that Muslim moves out of sight [with the impure object], then in the event that one deems it rationally probable that he has washed it, it is pure. This rule also applies to a non-bāligh child who is not mumayyiz as the child’s affairs are looked after by such a [Muslim] person entrusted with its affairs. Furthermore, things that a person cannot see because of a lack of light or being blind fall under the rule of becoming absent. Therefore, if the body or clothing of a Muslim becomes impure and someone does not see it being purified due to a lack of light or being blind, then in the event that he deems it rationally probable that it has been washed, it is ruled to be pure.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)