The Qur'aan itself refers to revelation being received from Allah that is not found in the Qur'aan and here are few examples:
Allah says in the Qur'aan, "And We made the Qiblah (prayer direction towards Jerusalem) which you used to face, only to test those who followed the Messenger (Muhammad)." [Soorah al-Baqarah (2): 143]
This verse shows that Allah had assigned the previous Qiblah of the Muslims but there is no verse in the Qur'aan designating Jerusalem as the previous Qibla. This means that there has to be an alternative form of 'Wahy' (revelation) apart from the Qur'aan through which Allah revealed the previous command of facing towards Jerusalem. This Command is in the Sunnah of the Prophet PBUH.
"And (remember) when the Prophet PBUH disclosed a matter in confidence to one of his wives (Hafsah), so when she told it (to another i.e. Aa'isha), and Allah made it known to him, he informed part thereof and left a part. Then when he told her (Hafsah) thereof, she said, 'Who told you this?' He said, 'The All-Knower, the All-Aware (Allah) has told me." [Soorah at-Tahrim (66): 3]
The verse says, "Allah made it known to him," and yet, there is no verse in the Qur'aan that makes mentions this.
To obey the Prophet is to obey Allah:
He who obeys the Messenger [Muhammad] has indeed obeyed Allah.. (Qur'an 4: 80)
Say [Muhammad to mankind]: 'If you [really] love Allah then follow me, Allah will love you and forgive you of your sins.' ...(Qur'an 3: 31)
See whoever follows the Prophets Sunnah follows Allah.
Do not hold the Messenger's calling (you) among you to be like your calling one to the other; Allah indeed knows those who steal away from among you, concealing themselves; therefore let those beware who go against his order lest a trial afflict them or there befall them a painful chastisement. (24:63)
