Some Imams say the closing salam on the right: (Peace be upon you and Allah's mercy and blessings), and on the left: (Peace be upon you and Allah's mercy)

The questioner : ...and Allah's mercy and blessings, and on the left I said: Peace be upon you and Allah's mercy. In many mosques, some Imams do this, while others are content with saying Peace be upon you and Allah's mercy on the right and on the left?

The Shaykh: Yes.

The questioner : So what is the most complete form in the prayer?

The Shaykh : The most complete form is what you heard. The Messenger (peace and blessings be upon him) had different forms of... the least and easiest of them was a single salam, not fully on the right like this, but rather he would turn his head slightly and say: Peace be upon you, and that was it, the prayer ended. The second salam, or the second form that the Messenger (peace and blessings be upon him) sometimes did, was: Peace be upon you and Allah's mercy, Peace be upon you, without the "and Allah's mercy" on the second one, and this is part of the etiquette of Islam... in distinguishing the right side from the left side. The third form is what you hear in all the mosques, equalizing the right and the left: Peace be upon you and Allah's mercy, Peace be upon you and Allah's mercy. The fourth and final form is what you heard on this night: Peace be upon you and Allah's mercy and blessings, Peace be upon you and Allah's mercy. This is the best of them. The meaning of all this is that the Messenger (peace and blessings be upon him) sometimes would say the salam like this, sometimes like this, sometimes like this, and sometimes like this. And we return to say: The best of guidance is the guidance of Muhammad (peace and blessings be upon him and his family).