It is reported from the Mother of the Believers, Sayyidah Aishah (may Allah be pleased with her), concerning the incident of the slander (al-ifk), that the Messenger of Allah (peace and blessings be upon him) was sitting; he removed the covering from his face and recited this verse: "'A'udhu billahi al-sami'i al-'alimi min al-shaytani al-rajim' (I seek refuge with Allah, who hears everything and knows everything, from Satan the accursed). 'Indeed, those who came with the slander' [Surah al-Nur: 11]."
(b) Abu Dawud said: I fear that the addition of the isti'adhah may be the words of Humayd.
(c) The Shaykh (may Allah have mercy on him) said that the Prophet (peace and blessings be upon him) recited "In the name of Allah, the Most Gracious, the Ever-Merciful" before beginning a surah, and he (peace and blessings be upon him) did not recite the Bismillah before verses which were not at the beginning of a surah. In this there is also confirmation of what we have reported from Ibn Abbas (may Allah be pleased with them both), that the Bismillah was written in the copies of the Qur'an only where it was revealed. And Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 2381