When was the ayah ‘I have today perfected your religion’ – ‘al-Yawm Akmaltu lakum Dinakum’ – revealed?

‘al-Yawm Akmaltu lakum Dinakum’, Qur’an 5:3, gave clear testimony to the perfection of
the religion of Islam, and announced the Imamah of Ali (A.S). It was revealed at Ghadeer Khum.
Ghadeer Khum lies in Juhfa, between Makkah and Madinah. Sunni and Shi’ah historians and scholars are unanimous about the event that took place there. When the Prophet (PBUH) was on his way home after his last pilgrimage, Jibra’il delivered the urgent command of Allah, O Apostle of Allah, deliver what has been sent down to you from your Lord for if you do not do this, [it will be as if] you have not have delivered His Message [at all]. Qur’an 5:67
When the Prophet (PBUH) ascended a dais of camel saddles he announced to the assembled Muslims that, ‘Ali is master – Mawla – of those over whom I am Mawla’.
The following Sunni scholars admit the authenticity of the above ahadith:
al-Tirmidhi (in his Sahih Vol. 2, p. 298),
al- Hakim (in al-Mustadrak Vol. 3, p. 109);
al-Tahawi (in Mushkilul-Athar Vol. 2, p. 308);
for further details refer to al-Amini (in al-Ghadir) Vol. 1, p. 295).