Sahih Bukhari Volume 004, Book 055, Hadith Number 633.
Narated By Ibn Abbas : The prostration in Sura-Sad is not amongst the compulsory prostrations, though I saw the Prophet prostrating on reciting The Statement of Allah: and to David We gave Solomon (for a son). How excellent (a) slave he was ever oft-returning in repentance (to us) (38.30) And His Statement: He said: My Lord Forgive me and grant me a kingdom such as shall not belong to any other after me.' (38.35) And His Statement: 'And they followed what the Devils gave out (falsely), of magic in the life-time of Solomon.' (2.102)