1 - Quran [2:238]حَافِظُوا عَلَى الصَّلَوَاتِ وَالصَّلَاةِ الْوُسْطَىٰ وَقُومُوا لِلَّهِ قَانِتِينَ
Guard strictly your (habit of) prayers, especially the Middle Prayer; and stand before Allah in a devout (frame of mind).
2 - Sunan Abi Dawud [#:921] Narrated AbuHurayrah: The Prophet (peace_be_upon_him) said: Kill the two black things during prayer, the snake and scorpion.
3 - Sunan Abi Dawud [#:924] Narrated Abdullah ibn Mas'ud: We used to salute during prayer and talk about our needs. I came to the Apostle of Allah (peace_be_upon_him) and found him praying. I saluted him, but he did not respond to me. I recalled what happened to me in the past and in the present. When the Apostle of Allah (peace_be_upon_him) finished his prayer, he said to me: Allah, the Almighty, creates new command as He wishes, and Allah, the Exalted, has sent a fresh command that you must not talk during prayer. He then returned my salutation.
4 - Sahih Bukhari [#:1129]Narrated Zaid bin Arqam: In the lifetime of the Prophet we used to speak while praying, and one of us would tell his needs to his companions, till the verse, 'Guard strictly your prayers (2.238) was revealed. After that we were ordered to remain silent while praying.
5 - Sahih Bukhari [#:1156]Narrated Abu Huraira: The Prophet led us in the `Asr or the Zuhr prayer and finished it with Taslim. Dhul-Yadain said to him, "O Allah's Apostle! Has the prayer been reduced?" The Prophet asked his companions in the affirmative. So Allah's Apostle I offered two more rak`at and then performed two prostrations (of Sahu). Sa`d said, "I saw that 'Ursa bin Az-Zubair had offered two rak`at in the Maghrib prayer and finished it with Taslim. He then talked (and when he was informed about it) he completed the rest of his prayer and performed two prostrations, and said, 'The Prophet prayed like this.' "