Sheikh Ahmad al-Khalîl, professor at al-Imâm University, Qasîm Branch
A divorce given in writing will be valid by as long as the man intended divorce. This is the case even if he does not pronounce the divorce verbally.
A divorce in writing is different than a verbal pronouncement in that the intention of effecting a divorce is necessary for the divorce to take place. By contrast, in a verbal pronouncement, his intention for divorce will not be necessary, since all that is required for a verbal pronouncement to take effect is the deliberate intention to make the pronouncement, even if only in jest.
The proof that a written divorce is valid is as follows. The Prophet (peace be upon him) said: “Allah has forgiven my people for what they say within themselves unless they talk about it or act upon it”.
As this man wrote down his statement of divorce, he has acted, and thus his divorce will be valid.
And Allah knows best.
Source: Islam Today