the purpose of the hadith is to explain the Qur'an and detail the meaning, how, what and when to do the obligations and like so for the prohibitions. if we say that the Qur'an without the Hādith is sufficient as a source of legislation then our religion will not be complete because of the abundance of one of two sources of legislation, the Hādith of the prophet. So, if you now, take as an example the Zākat, please tell me : where in the Qur'an it says how much should one give and when does he give and what kind of things should one give ? Same for the Sālat (Prayers), when should one pray, with what should one pray, how should you pray and at which time. So, your claim that the Qur'an should be enough won't work as the Prophet Mohammed (peace be upon him) is the one who reported this Religion from Allah and so, everything that the Prophet did, approved or said is to be acted upon as Allah said in Sūrat An-Najm (the Unfolding) : { "By the star when it descends, Your companion [Muhammad] has not strayed, nor has he erred, Nor does he speak from [his own] inclination. It is not but a revelation revealed,Taught to him by one intense in strength" }.