Shaikh al-Albani rahimahullah was asked:
Question: Is it allowed to perform a surgery to change the condition of a person from a man to a woman and vice versa?
Answer: “The answer to this is understood from what has preceded:
فطرة الله التي فطر الناس عليها لا تبديل لخلق الله
Allah’s Fitrah (i.e. Allah’s Islamic Monotheism), with which He has created mankind. No change let there be in Khalq-illah [30:30]”
[Ashritah al-Mutafarriqah no. 167]
The Permanent Committee have also ruled sex-change operation’s to be impermissible as can be found here
Faisal Ibn Abdul Qaadir Ibn Hassan