There is not a certain ruling about oral sex in Islam. However, it is against the unspoiled human nature. Therefore it is makruh.
If we read the 222nd and 223rd verses of Surah Al-Baqarah, you will understand that anal sex is not permitted. (See http://www.islamandquran.org/fatwas/is-anal-sex-forbidden.html for further information.) The hadiths of our Prophet that ban the anal sex should be understood accordingly. Although oral/using mouth sex is not recommended, it is not a type of intercourse from front or back genital organs. If it were for it, information that ban this type of intercourse would have reached us just like the hadiths that ban anal sex.
The evidence of the scholars that do not tolerate this, is the concern of infection risk.
Since there is not an absolute evidence like a verse or a hadith on this subject, oral sex is counted as makruh. Makruh is not like haraam. Haraam is what is forbidden by a certain ruling (hukm).
All words, actions, behaviours and deeds that are not explicitly forbidden by either Qur’an Al-Karim or Sunnah are halal and can be performed. Making haraam (forbidden) what is actually halal is putting ourselves in God’s shoes, just like making halal (lawful) what is forbidden. It is one of the greatest sins. We will deal with this topic in this sensitivity.
Oral sex was a known type of intercourse in the Prophet’s era, in the meaning of sucking spouses’ sexual organs. We learn it by the words of Abu Bakr (r.a.) that he said to Urva b. Masud, the messenger of Quraish, as a well known invective amongst Arabs, during the negotiations of Hudaybiyya: “Oh man, deserves to suck the clit of Lat idol (Female)” (Tajrid 8/176.)
Though it is known as a technique of foreplay, there is not a clear ruling about it in Qur’an and Sunnah. However, general rules apply. Oral sex must be investigated in two parts.
a) Oral sex which is performed at the beginning of sexual intercourse without smearing the semen or pre-seminal fluid on tongue or teeth, may be approved. Because it would not cause psychological depression.
On the other hand, a spouse who is against or not interested in oral sex due to cultural or psychological improvement reasons, should not be forced to do it. Since it. Since it may cause sexual unhappiness or even depression, that would be zulm to do. This kind of zulm is also haraam, just like sadism. Since oral intercourse is not an ordinary type of sexual relation, it may cause feelings like hatred or disgust in long term, and therefore may cause sexual unhappiness. Thus, we recommend staying away from this type of -approvable- oral sex, too. There are known scholars who recommend staying away from it.
b) Oral sex which uses mouth as a sexual organ and allows ejaculation into mouth is – Allah knows the best – is haraam.
Qur’an and Sunnah forbid sexual intercourse from the back passage. It is obvious that they would absolutely forbid intercourse with the use of mouth, as they even inform that making anal sex lawful is a reason to be tormented. Besides, this type of intercourse would be disgusting for unspoiled human nature. It is ‘fah-shaa’ and ‘khabis’ by the words of Qur’an. Sexual related evil – ‘fah-shaa’- and dirty things ‘khabis’ are forbidden -made haraam- by the Qur’an.
Allah knows the truth best. As believing servants of Him, we should refrain from anything that is even suspected to be haraam.
To summarize: Approvable oral intercourse is of types kissing and sucking. We can tell that the type including ejaculation into mouth is evil and forbidden. Because it is fah-shaa and khabis, which is forbidden by Qur’an.”
(Resource: Ali Rıza Demircan, İslam’a Göre Cinsel Hayat, Beyan Yayınları, İstanbul, 2008, p: 186-187)