The word(s) "observe" appears 49 time(s) in 47 verse(s) in Quran in Muhammad Pickthal translation.

(21) Lo! We did reveal the Torah, wherein is guidance and a light, by which the prophets who surrendered (unto Allah) judged the Jews, and the rabbis and the priests (judged) by such of Allah's Scripture as they were bidden to observe, and thereunto were they witnesses. So fear not mankind, but fear Me. And My revelations for a little gain. Whoso judgeth not by that which Allah hath revealed: such are disbelievers.

(22) If they had observed the Torah and the Gospel and that which was revealed unto them from their Lord, they would surely have been nourished from above them and from beneath their feet. Among them there are people who are moderate, but many of them are of evil conduct.

(23) Say O People of the Scripture! Ye have naught (of guidance) till ye observe the Torah and the Gospel and that which was revealed unto you from your Lord. That which is revealed unto thee (Muhammad) from thy Lord is certain to increase the contumacy and disbelief of many of them. But grieve not for the disbelieving folk.

(24) When the disciples said: O Jesus, son of Mary! Is thy Lord able to send down for us a table spread with food from heaven? He said: observe your duty to Allah, if ye are true believers.

(25) And they observe toward a believer neither pact nor honour. These are they who are transgressors.

(26) He only shall tend Allah's sanctuaries who believeth in Allah and the Last Day and observeth proper worship and payeth the poor-due and feareth none save Allah. For such (only) is it possible that they can be of the rightly guided.

(27) Have they not observed all things that Allah hath created, how their shadows incline to the right and to the left, making prostration unto Allah, and they are lowly?

(28) And thou wouldst have deemed them waking though they were asleep, and We caused them to turn over to the right and the left, and their dog stretching out his paws on the threshold. If thou hadst observed them closely thou hadst assuredly turned away from them in flight, and hadst been filled with awe of them.

(29) And she said unto his sister: Trace him. So she observed him from afar, and they perceived not.

(30) And (the tribes of) A'ad and Thamud! (Their fate) is manifest unto you from their (ruined and deserted) dwellings. Satan made their deeds seem fair unto them and so debarred them from the Way, though they were keen observers.