Qabd al-yadayn

Leading Sunni Shaikh Sayyed Saabiq of Al-Azhar stated that there is no single Hadeeth which can be considered as authentic suggesting that the Prophet (SAWA) ever crossed his hands during Salah (Fiqh Al-Sunnah).  That is why you find none of Sunnis is claiming folding or crossing the hands during Salah as Wajib and you find different verdicts among them. Imam Malik who is one of the four main Sunni Imams stated that the Salah of the Prophet (SAWA) and his companions after him is with open hands and never with holding or crossing hands. Imam Malik was asked about crossing hands in Salah, he replied: I don't know it , which means that it was not practiced by the Prophet nor his companions. (Al-Moghni by Ibn Qudamah, page 514).
'This crossing or folding hands was ordered first by Omar ibn al-Khattab when prisoners of war were brought from Persia to Madina and they did that as it was part of their culture or religious practice when they saw him as a sign of respect to the head of the state. He liked it and ordered his people to do it in Salah.(Jawahir Al -Kalam, V.11, page 19). Many leading companions rejected it as it was never done or approved by the Prophet (SAWA).

Imam Ali (AS) who is the best who knows about the Prophet, has repeatedly objected on crossing hands and called it emitting non Muslims as Jewish and Majoos fold their hands during their prayer. Imam Ali (AS): أسبلوا ولا تتشبهوا باليهود. أسبلوا ولا تتشبهوا بالمجوس Pray with your hands open and never imitate Jewish people. Keep your hands open while praying and never resemble Majoos.

Wassalam.

Woman is recommended to put her hands separately on the two sides of her chest. That is not folding hands at all. 
Wassalam.

1, Folding arms while praying was never practiced nor permitted by the Prophet Muhammad (SAWA). It was started by Omar Ibn al-Khattab when he saw the Zoroastrian prisoners of war who were brought from Persia to Madina folding their arms as a sign of respect. He ordered people to do that during Salah. Leading Sunni scholars like Ibn Rushd in Bidayat al-Mujtahid page 323 admitted that there is no evidence at all that the Prophet (SAWA) ever folded his hands or arms during praying.
Sunni well know scholar Malik ibn Anas who is the founder of Maliki Sunni sect refused this practice of folding hands while praying.

'Many well known Sahaba (Companions) refused folding hands like Ibn Abbas, Ibn Mas'ood, and above all and most importantly Imam Ali (AS) who was ordering Muslims to do this practice which is from non Muslims.

2.Sajdagah: We follow the real Sunnah of the Prophet Muhammad (SAWA) who never prostrated during prayers on carpet or textile and used to put his forehead on the earth. He said: The earth was made for me as place for prostration and purification. جُعِلت لى الأرض مسجدا وطهورا 

That is why we put Sajdagah to put our forehead on the clay of the earth like the practice of the Prophet (SAWA).

Wassalam.

The habit of folding ( crossing) 

hands during Salaah came from non-Muslims (notably Zoroastrians) and wasn’t part of the Salaah of the Holy Prophet (sawa), nor during the government of Abu Baker. However, during the rule of Umer ibn Khattab, when Persia was concurred by Muslims, several prisoners of war were brought from Persia to Madina. They folded their hands in front of Umer, who asked them why they did so. They responded that it was their habit in front of respected people. Umer liked it and decided to keep it in the prayer. Ali ibn Abi Talib (a.s) and many of the Sahaba refused this, because no one has the right to change or add or to omit anything from the Salaah, and the Prophet (sawa) had famously said, “Pray as you saw me praying.
Therefore Amir ul Mo’mineen (a.s), his followers (Ammar ibn Yasir, Salman al Farsi, Abu Dhar al Ghifari) and all of his other pious companions continued opening their hands while praying, exactly like the Prophet (s) used to. 
In the Sunni school of thought, none of the four leading jurists (Abu Hanifa, Shafi’i, Malik ibn Anas, Ahmad ibn Hanbal) ever said that it was obligatory to fold hands during Salaah, because there was no evidence to support it. Imam Malik even said it was not good to fold hands, and all Malikis thus open their hands in Salaah. A famous Sunni ‘Aalim from Egypt, Sayyid Sabiq, wrote in his book Fiqh as Sunnah: “we do not have even a single authentic Hadith that the Prophet (s) ever folded his hands in the Salaah.
 Numerous famous individuals from the Sunni school of thought such as Abdullah ibn Zubayr and Laith bin Saad didn’t fold their hands either. Folding hands in Salaah was therefore not part of Islam, it was brought to Muslims from non Muslims by Umer ibn Khattab.

Wassalam.