Placement of the hands in prayer between Ahl al-Sunnah and others
Question

I am confused between the way a Sunni prays and the way a Shi'te prays. My father is a Shi'te and he has taught me to pray with my hands on my sides but I do not know what is the differnce. Why is there such difference between the two? Also, I would be very grateful if you tell me which form was used originally by Mohammad.
Praise be to Allah.1 – The difference between the Shi’ah (Raafidis) and Sunnis (Ahl al-Sunnah) is very great, because of the difference in the sources to which each group refers. The Shi’ah rely on books and scholars who are insignificant in the eyes of the Sunnis. 
For example, after the Quran, the Sunnis rely on Saheeh al-Bukhari, but the Shi’ah do not regard it as a reference and they do not regard its author as significant. They even differ from us with regard to the Sahaabah. The Shi’ah regard all the Sahaabah as kaafirs apart from a few of them. Some of them even claim that the Quran which is in circulation among the Sunnis is missing some parts and has been altered; those who do not say that the Quran is missing some parts and has been altered say that it has been misinterpreted and reject the tafseer (interpretation) that has been narrated from our imams. 
Al-Shu’bi said: I warn you against misguided groups, the worst of which are the Raafidis. ‘Ali ibn Abi Taalib burned them with fire and expelled them from the land, and the proof of that is that the ideas of the Raafidis are like the ideas of the Jews. 
The Jews said that only a man from the family of Dawood could be a leader, and the Raafidis say that only a man from among the descendents of ‘Ali ibn Abi Taalib could be a leader. 
The Jews said that there can be no fighting for the sake of Allah until the Dajjaal (“Antichrist”) appears and some support comes down from heaven, and the Raafidis say that there can be no fighting for the sake of Allah until the Mahdi appears and a voice calls out from heaven. 
The Jews delay the evening prayer until the stars appear, and the Raafidis do likewise. According to a hadeeth narrated from the Prophet SAWS (peace and blessings of Allah be upon him): “My ummah will continue to adhere to the fitrah (sound natural disposition of man) so long as they do not delay Maghrib prayer until the stars appear.” (Abu Dawood, 418; Ibn Maajah, 689; classed as saheeh by al-Albaani in Saheeh Abi Dawood, 444). 
The Jews turned away slightly from their direction of prayer, as do the Raafidis. 
The Jews sway back and forth in prayer, as do the Raafidis. 
The Jews regard it as permissible to shed the blood of every Muslim, as do the Raafidis. 
The Jews do not observe any ‘iddah (waiting period) when a woman is divorced or widowed, and neither do the Raafidis. 
The Jews reject the idea of three-fold talaaq (divorce), as do the Raafidis. 
The Jews altered the Tawraat (Torah), as the Raafidis altered the Quran. 
The Jews hate Jibreel and say, “He is our enemy among the angels.” Some of the Raafidis do likewise and say that he made a mistake by giving the Revelation to Muhammad (peace and blessings of Allah be upon him). 
Al-Sunnah by al-Khallaal, 3/497-498. 
These are some of the misguidance and myths of the Shi’ah. Hence it is no surprise that they put their arms at their sides when praying, which is clearly contrary to the saheeh Sunnah.
 With regard to the evidence for placing the right hand over the left when praying, there is a great deal of such evidence.  For example: 
It was narrated that Sahl ibn Sa’d said: The people were commanded to put the right hand over the left forearm when praying. 
Abu Haazim said: I only know that this is attributed to the Prophet (peace and blessings of Allah be upon him). (Narrated by al-Bukhari, 707). 
“[The Prophet] (peace and blessings of Allah be upon him) used to place his right hand on his left hand.” (Narrated by Muslim, 401). 
The Messenger of Allah (peace and blessings of Allah be upon him) passed by a man who was praying, and who had placed his left hand on his right hand. He grabbed his arms and put his right hand on his left.” (Ahmad, no. 12671) 
It was narrated from Waa’il ibn Hajar that he saw the Prophet (peace and blessings of Allah be upon him) raise his hands when he started to pray and say Takbeer, and according to Hammaam he raised his hands level with his ears.  Then he wrapped his hands in his garment, putting his right hand on his left. When he wanted to bow in rukoo’ he took his hands from beneath his garment, raised them, then said Takbeer and bowed. When he said “Sami’a Allah liman hamidah,” he raised his hands, and when he prostrated, he prostrated between his two hands.” (Narrated by Muslim, 401). 
It was narrated that Ibn ‘Abbaas (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “We Prophets have been commanded to hasten the breaking of our fast and to delay our suhoor, and to put our right hands over our left when praying.” (Narrated by Ibn Hibbaan, 3/13. This hadeeth was classed as saheeh by Shaykh al-Albaani in Sifat al-Salaah, p. 87). 
Ibn Hajar said: 
Ibn ‘Abd al-Barr said: There is no different report narrated from the Prophet (peace and blessings of Allah be upon him), and this is the view of the majority of the Sahaabah and Taabi’een. This is what was mentioned by Maalik in al-Muwatta’, and Ibn al-Mundhir and others did not narrate anything different from Maalik. Ibn al-Qaasim narrated that Maalik had said that the arms should be held at the sides, and most of his companions followed him. And it was narrated that he said there is a difference between obligatory and naafil prayers. Some of them regarded it as makrooh to hold one hand with the other. Ibn al-Haajib narrated that this means it is makrooh when one does it for the purpose of resting the hands.”
 Fath al-Baari, 2/224.
 And Allah knows best.