1- There is a Hadith that says that if we see a black flag from Khorasan then we should go to it even if we had to crawl on ice/snow because Imam Mahdi is with them. Is this Hadith Sahih or Hasan?2- Can we sit with a group of people making Bidah? What does our Prophet (S.A.W)and our pious predecessors say on this matter?3- While giving Adhan should we turn our head to the left or the right when we say haya ala a assalaat and haya alllfalah? Was it done during the time of our Prophet?4-Can we see Houries in dreams?

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
1. As for the Hadith asking about the Mahdi it is narrated by Ibn Majah and Al Hakem from Thowban that the Prophet said: "Three men, all of them sons of Caliphs (rulers), will fight over your treasure and none of them will take it. Then black flags will appear in the Orient, they will kill you in a manner in which no one had been killed before. Thowban added the Prophet said something else that I do not remember very well, then the Prophet said: "When you see this (man) pledge allegiance to him even if this requires you to crawl on snow as he is the Caliph of Allah, Al Mahdi". Ibn Katheer described this Hadith as sound.
Al Albani said the meaning of this Hadith is sound except this last expression: "as he is the Caliph of Allah, Al Mahdi".
The "treasure" mentioned in this Hadith is the treasure of Al Kaaba. Three Caliphs will fight one another to get this treasure. When the last Day approaches, Al Mahdi will appear in the Orient not from Samurra's tunnel as claimed by some ignorants who even think that he is now there. Al Mahdi will be supported by some people from the Orient. They will appoint him Sultan (Muslim ruler). Their flags will be black and this colour is worth respect as it is the colour of the Prophet's flag, which was called: Al Iqab". (Al Nihaya) Ibn Katheer.
2. Sitting with people who are known to make bida' (innovations). The rule concerning this issue differs depending on the intention behind this sitting and on the bid'a itself (how bad and dangerous it is). If the person sits with such people to advise them or to show them the right way and explain to them the bad things they are performing, it is lawful. But if the person approves of the Bid'a and sits with those who do it because he likes them, it is then forbidden.
The evidence for not sitting or socializing with people who make bid'a (innovations) is the story of the three men who did not attend Tabuk ( a battle against the Romans led by the Prophet) and how the Prophet and his companions dealt with them. The Prophet avoided dealing with them for fifty days until Allah revealed to him that He has accepted their repentance.
Moreover, the Prophet cursed anybody who gives shelter to an "innovator". Abu Tufail 'Amir b. Wathila reported: I was in the company of 'Ali b. Abu Talib, when a person came to him, and said: What was it that Allah's Apostle (May peace be upon him) told you in secret? Thereupon he (Ali) was enraged and said: Allah's Apostle (May peace be upon him) did not tell me anything in secret, that he hid from people, except that he told me four things. He said: Commander of Faithful, what are these? He said: Allah cursed him who cursed his father; Allah cursed him who sacrificed for anyone besides Allah; and Allah cursed him who accommodates an innovator (in religion); and Allah cursed him who changed the minarets (the boundary lines) of the land". [Reported by Imam Muslim].
Some scholars limited this cursing to any person who gives shelter to an innovator in Madina exclusively for the other Hadith 'Asim reported: I asked Anas b. Malik whether Allah's Messenger (May peace be upon him) had declared Medina as sacred. He said: Yes, (the area) between so and so. He who made any innovation in it, and further said to me: It is something serious to make any innovation in it (and be who does it) there is upon him the curse of Allah, and that of the angels and of all the people, Allah will not accept from him on the Day of Resurrection either obligatory acts or the supererogatory acts.
3. It is a Sunnah that the Muezzin turns his head right and left when saying: "Haya Ala Salat" 'Haya Ala Al Falah', for the Hadith narrated by Al Bukhari.
The scholars differed over how the Muezzin moves his head. But the majority of them believes that he says: Haya Ala Salat twice while turning his face right then he says "Haya Ala Al Falah" twice while looking left. While turning, he moves only the head, neck and chest without moving his feet.
4. A Muslim can see Houries in his dreams since there is nothing in Sharia, which contradicts this possibility.
Allah knows best.