The Prophet's sole mission was to deliver Quran, the whole Quran, and nothing but Quran (3:20; 5:48-50, 92, 99; 6:19; 13:40; 16:35, 82; 24:54; 29:18; 42:48; 64:12).
Delivering the Quran was such a momentous and noble mission that the Prophet did not have any time to do anything else. Moreover, the Prophet was enjoined in the strongest words from issuing any religious teachings besides the Quran (69:38-47). He was even enjoined from explaining the Quran (75:15-19) - God is the only teacher of the Quran (55:1-2) and the Quran is the best Hadith (39:23 & 45:6).
These Quranic facts are manifested in the historical reality that the words and actions (Hadith & Sunna) attributed to the Prophet did not appear until the second century after his death. The Quran has prophesied the fabrication of Hadith and Sunna by the Prophet's enemies (6:112-115). The Quran teaches us that it was God's will to permit the invention of Hadith and Sunna to serve as criteria for exposing those who believe only with their lips, not in their hearts. Those who are attracted to Hadith and Sunna are proven to be false believers (6:113). Ironically, the books of Hadith report the Prophet's orders to write down nothing from him except the Quran! Shown below are two such Hadiths taken from the Hadithists' most reliable sources, Sahih Muslim and Is-haah Ahmad Ibn Hanbal: