Verses from Quran on being united

“And hold fast altogether to the rope of Allaah and do not be divided.” [Soorah Aali-’Imraan 3:101]
“And do not be like those who split-up and differed after the clear evidences came to them. For them is a tremendous punishment.” [Soorah Aali-’Imraan 3:105]
“And this is My Straight Path, so follow it and do not follow other paths that will separate you from His Path. This has He ordained for you, that you may become pious.” [Sooratul-An’aam 6 :153]
“Indeed those who spilt-up their Religion and become sects, you have no part with them in the least. Their affair is with Allaah who will tell them what they used to do.” [Sooratul-An’aam 6:159]
If anyone contend with the Messenger even after guidance has been plainly conveyed to him, and follows a path other than that becoming to men of faith, We shall leave him in the path he has chosen, and land him in Hell – what an evil refuge! [Sooratun-Nisaa aayah 115]
The Prophet (sallallaahu ‘alayhi wa sallam) said: “The best of people is my generation and then those follow them and then those who follow them, then lies will be widespread.” Saheeh: Related by al-Bukhaaree (no. 2652) and Muslim (no. 2533 ).
Anas (ra) reports that the Prophet (sallallaahu ‘alayhi wa sallam) said : “…. And my Ummah will divide into 73 sects, all of them in the fire, except for one.” So it was said: ” O Messenger of Allah, who are they?” so he said: “They are those who are upon what I am upon today and my companions.” Ibn Maajah, declared Saheeh by Shaykh al-Albaani