Blessing the Prophet (saws)

His son narrated that Abu Hamza said: I, once, asked Imam as-Sadiq (a) about the exegesis of God’s saying:
“Allah showers His blessings upon the Prophet and the angels, too, do. Believers, pray for the Prophet and greet him thoroughly. (33:56)”
He answered: “The blessing of Allah is mercy to the Prophet (s), and the blessing of the angels is purification to him, and the blessing of people is supplication for him. To ‘great him thoroughly,’ means to submit to that whichever is –authentically- re lated to him.”
I asked: “How should we bless Mohammed and his family?” The Imam (a) replied: “You should say:

صَلَواتُ اللهِ وَصَلَواتُ مَلائِكَتِهِ وَأَنْبِيائِهِ وَرُسُلِهِ وَجَميعِ خَلْقِهِ عَلى مُحَمَّدٍ وَآلِ مُحَمَّدٍ ، وَالسَّلامُ عَلَيْهِ وَعَلَيْهِمْ وَرَحْمَةُ اللهِ وَبَرَكاتُهُ.

‘The blessings of Allah and the blessings of His angels, prophets, messengers, and all creatures be upon Mohammed and the family of Mohammed. And peace and Allah’s mercy and blessings be upon him and them.’”
I asked: “What is the reward that one will win if he utters such blessings for the Prophet and his family?”
The Imam (a) answered: “The reward is that he will be acquitted from all of his sins, as if he has just left his mother’s womb.” Bihar ul-Anwar; 19/78 (as quoted from Meaani al-Akhbar) ) 

Reference :The Ahl Ul-Bayt Ethical Role-Models