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

(41) Have ye observed the fire which ye strike out;

(42) We verily sent Our messengers with clear proofs, and revealed with them the Scripture and the Balance, that mankind may observe right measure; and He revealed iron, wherein is mighty power and (many) uses for mankind, and that Allah may know him who helpeth Him and His messengers, though unseen. Lo! Allah is Strong, Almighty.

(43) Then We caused Our messengers to follow in their footsteps; and We caused Jesus, son of Mary, to follow, and gave him the Gospel, and placed compassion and mercy in the hearts of those who followed him. But monasticism they invented - We ordained it not for them - only seeking Allah's pleasure, and they observed it not with right observance. So We give those of them who believe their reward, but many of them are evil-livers.

(44) Hast thou not observed those who were forbidden conspiracy and afterward returned to that which they had been forbidden, and (now) conspire together for crime and wrongdoing and disobedience toward the messenger? And when they come unto thee they greet thee with a greeting wherewith Allah greeteth thee not, and say within themselves: Why should Allah punish us for what we say? Hell will suffice them; they will feel the heat thereof - a hapless journey's end!

(45) Hast thou not observed those who are hypocrites, (how) they tell their brethren who disbelieve among the People of the Scripture: If ye are driven out, we surely will go out with you, and we will never obey anyone against you, and if ye are attacked we verily will help you. And Allah beareth witness that they verily are liars.

(46) O ye who believe! observe your duty to Allah. And let every soul look to that which it sendeth on before for the morrow. And observe your duty to Allah. Lo! Allah is Informed of what ye do.

(47) Hast thou observed him who belieth religion?