Actually this is based on Koran 4:92, which forbids Muslims to kill other Muslims. But Infidels are fair game. "Saudi University Professor Salman Al-Abdali: Suicide Bombings Okay in Tel Aviv, Not in Riyadh," from [1] MEMRITV, October 1 (thanks to [2] Weasel Zippers):

Following are excerpts from an interview with Saudi University professor Salman Al-Abdali, which aired on Iqra TV on October 1, 2009. [...]

Someone who blows himself up amidst the enemy is different from someone who blows himself up in a safe place. Blowing oneself up in Tel Aviv is not like blowing oneself up in Riyadh.