Wiping the face after du`a and placing the hand over the heart after greeting someone
Question

I have noticed with some of my freinds, especially the ones from Malaysia, that straight after they say the taslim in salat, they rub their hands over their faces...is this correct or is bid'a?? and also, with malay people, when they greet you and they shake your hand, they then pass their hand over their heart...is this also correct or is it bid'a? i would really appreciate your answer... and also...if it is wrong for them to do this...how should i tell them...is there any ahadith i could quote to them or some ayat from the Quran?.
Praise be to Allah.Firstly: 
It is not prescribed to place the hands over the face after finishing prayer or after finishing du`a. The best of guidance is the guidance of our Prophet Muhammad (peace and blessings of Allah be upon him). When he said the salaam (at the end of prayer) he would pray for forgiveness three times, but he did not wipe his face with his hands after saying the salaam or after saying du`a. 
It was narrated that Thawbaan (may Allah be pleased with him) said: When the Messenger of Allah (peace and blessings of Allah be upon him) had finished his prayer, he would pray for forgiveness three times, and say: “Allahumma anta al-salaam wa minka al-salaam, tabaarakta yaa dhaa’l-jalaali wa’l-ikraam (O Allah, You are al-Salaam (the One Who is free from all defects and deficiencies) and from You is all peace, blessed are You, Possessor of majesty and honour)”. Narrated by Muslim (591). 
In the answer to question no. 39174 we stated that it is not prescribed to wipe the face with the hands after saying du`a. 
Secondly: 
Shaking hands is something that is mentioned and encouraged in sharee’ah, and it is a cause of sins being forgiven. 
It was narrated that al-Bara’ ibn ‘Aazib (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “There are no two Muslims who meet and shake hands, but they will be forgiven before they part.” Narrated and classed as hasan by al-Tirmidhi (2727); narrated by Ibn Maajah (3703); classed as saheeh by al-Albani in Saheeh al-Targheeb, 2718. 
Some people put their hands over their hearts after greeting and shaking hands with someone, but this is contrary to the meaning of shaking hands both in linguistic terms and in Islamic terminology. There is no evidence for that in the Sunnah, and there is no report – as far as we know – which says that any of the salaf did that. 
Shaking hands means clasping the palm of one hand against the palm of the other person’s hand. 
Al-Raaghhib al-Asfahaani said: 
Shaking hands means stretching the palms of the hands (against one another). 
Ghareeb al-Quran (1/282). 
And Ibn Hajar al-‘Asqallaani said: 
Shaking hands means clasping the palm of one hand against the palm of the other hand. 
Fath al-Bari (11/54) 
Shaking hands is sufficient to greet a person in accordance with the Sunnah. However, if the people are accustomed to placing the hand over the heart after shaking hands or greeting someone as a way of showing honour to them, then we hope that there is nothing wrong with it, but we should not attribute that to the Sunnah of the Prophet (peace and blessings of Allah be upon him), rather a person may do it on the basis that it is customary and not the Sunnah of the Prophet (peace and blessings of Allah be upon him). 
And Allah knows best.