Can sunnis and shias pray together?

Answer 1

This is highly unlikely. The Divisions between Sunnis and Shiites have persisted for centuries. Once a religious sectarian division comes into existence it is impossible to theologically heal it unless at least one side concedes that its position on the theological issues that the two sects disagree on is wrong. However, a theological union is not necessary for a political or social union, so it is worth asking why the two groups remain politically and socially acrimonious. (Note that the majority of Sunnis and Shiites do not feel this way, but a large vocal minority in each camp still do.) There are several reasons for this animosity.

1) Historical Grievances: The primary reason this division persists is that there has never been an atonement by either side for the pain and persecution that it has suffered when the other was in power over a given territory. Although, Shiites endured more persecution at the hands of Sunnis than the reverse, this is not to say that Sunnis have not endured persecution at Shiite hands. Both groups remain defiant that since they have the moral high-ground as granted from their faith, their actions in repressing the other sect, torturing its adherents, and murdering its leaders was progress towards removing the heresy. Compare this to the Catholics, who have apologized for the Rape of Byzantium, which was huge historical grievance between them and the Orthodox.

2) Ethnic Identities: In many countries, especially Iraq, Syria, and Lebanon, people identify "ethnically" by their sect of religion. Therefore saying somebody is Shiite in Iraq is similar to how people view being Irish-American or Japanese-American in the United States. It marks you socially and it determines who your friends are, who you marry, what jobs you take, who you love, who you despise, etc. As a result, whenever conflict has broken out, each religious group comes together to defend its people's interests. This results in political and social hatred of the other religion in addition to any theological issues.

3) Rumors of the Other's Theology: Some Sunnis think that Shiites are deluded into believing that 'Ali was a second prophet, which would violate Mohammed being the final capstone of the Prophets, a huge theological issue. Some Shiites believe that Sunnis were paid off to accept the three Rightly-Guided Caliphs before 'Ali and that Sunni Islam was therefore corrupt and ineligible to continue the Islamic tradition. Both have alleged the other was deceived by Jews, which says more about how Muslims view Jews than each other. Of course, both of these are mis-characterizations of the actual theologies of these two sects, but the point remains that as long as these problematic rumors exist, the two sides cannot reconcile.

4) Approaches to Government: Ever since the abolition of the Caliphate in 1936, Sunni Islam has been leaderless and there has come to be an understanding that religion does not participate in actual governance. (This is not a separation of church and state since the two can cooperate closely, but this prevents direct theocracy.) Shiites, on the other hand, have religious leaders called Ayatollahs who do attempt to have terrestrial authority and in Iran have actually achieved it.

Answer 2

According to Shia Islam yes.