The word(s) "observe" appears 3 time(s) in 3 verse(s) in Quran in Muhammad Habib Shakir translation.

(1) To every nation We appointed acts of devotion which they observe, therefore they should not dispute with you about the matter and call to your Lord; most surely you are on a right way.

(2) Then We made Our apostles to follow in their footsteps, and We sent Isa son of Marium afterwards, and We gave him the Injeel, and We put in the hearts of those who followed him kindness and mercy; and (as for) monkery, they innovated it-- We did not prescribe it to them-- only to seek Allah's pleasure, but they did not observe it with its due observance; so We gave to those of them who believed their reward, and most of them are transgressors.

(3) The likeness of those who were charged with the Taurat, then they did not observe it, is as the likeness of the ass bearing books, evil is the likeness of the people who reject the communications of Allah; and Allah does not guide the unjust people.