Sunnah.com reference : Book 2, Hadith 235English translation : Book 2, Hadith 0Arabic reference : Book 2, Hadith 335
And in the narration of al-Bukhari:
'he should complete (the prayer) then he should say Taslim and then perform the prostration'.
وَفِي رِوَايَةٍ لِلْبُخَارِيِّ : { فَلْيُتِمَّ , ثُمَّ يُسَلِّمْ , ثُمَّ يَسْجُدْ }  .‏  1‏‏1 ‏- صحيح .‏ رواه البخاري ( 1 /504 / فتح )‏ .‏