There is no any formula to adopt in uniting the Ummah other than the one stated by Allah;

Say: 'People of the Book, let us come to a common word between us and you that we will worship none except Allah, that we will associate none with Him, and that none of us take others for lords besides Allah.' If they turn away, say: 'Bear witness that we are Muslims.'

The Ummah can only be united when all the people of wrong aqeedah, those the kill innocent souls (the khwarij) those that call on awliya’, (the sufis) the grave worshippers, those that are guilty of bid’ah, when they abandon their ways and stick to them to Sunnah of the Prophet S