Well, I don't know - lets see what that noted Muslim Theocrat and ruler of Iraq Ali Al-Sistani has to say on the subject -
A Question and Answer on the subject from his web site:
No: 1
Question:If my wife wants me to masturbate in front of her, is it then allowed?
Answer:You are not allowed to do it with hand, but your wife is.
No: 2
Question:Can woman cook for Nathr in monthly period?
Answer:Yes, it is permissible in both cases.
No: 3
Question:Is it ok to delay namaaz for a majlis or matam?
Answer:Prayers offered on time are much better. {Meaning, there is more significance in them.}
No: 4
Question:What does Islam say about masturbation? If a man is doing this what type of punishment will he deserve and how can he do\ get Tawba?
Answer:He has committed a forbidden act. Repentance would be sufficient for Tawbah.
No: 5
Question:When I am unable to do Muta’h (temporary marriage), am I allowed to masturbate?
Answer:Masturbation is not permissible under any circumstances.
http://www.sistani.org/html/eng/main/index.php?page=4&lang=eng&part=1