Should I cite a paper when a sentence is not a findings of a research work but mentioned in the paper? Problem

In the methodology section of this paper, authors mentioned that 


  Compared to other social network sites such  as  Facebook  and 
  Twitter,  Instagram  has  been  less  studied and understood.


I need to cite a sentence like this. However, this is not a findings of this paper. 

My Question

Will it be okay, if I cite this sentence?
If you take others work then you need to cite it. Otherwise it is called plagiarism.