Hadrat Imâm-i Rabbânî says in the  67th letter of the second volume of his Maktûbât:

Angels are Allah’s dear slaves. It is not possible for them to disobey Allah’s commands. They do what they are commanded. They do not get married. They do not bear children or multiply. Allâhu ta’âlâ has chosen some of them as prophets. He has honoured them with the task of carrying wahy. They are those who brought the Books and Suhûf to prophets. [For example, An’âm Sûra was brought by Hadrat Jebrâil (Gabriel) together with seventy thousand angels.] They do not make any mistakes, nor do they ever forget. They do not play tricks or deceive. What they bring from Allâhu ta’âlâ is always true. It is never doubtful, nor does it depend upon probabilities. Angels are afraid of Allah’s grandeur, wrath and greatness. They have no other work than doing what they are commanded.

Sin is not to do Allah’s commandments and not to abstain from His prohibitions. Commandments and prohibitions are for Muslims, for those who have îmân. He has not honoured those who have no îmân, disbelievers, with commanding them or making them worship. Like animals, they do what they wish, and it is not a sin. They are not tormented in the world for not worshipping, for sinning; they get every kind of blessing; they obtain what they wish and work for. Only, the cruel ones, those who torment creatures, get their deserts in the world. Disbelievers have been commanded one thing only, they have been asked to do one thing only. This one thing is having îmân, becoming Muslim. Disobeying this one command, disbelievers have committed only one crime. Yet, it is the gravest crime. The penalty for the crime is very great, very bitter and endless. There cannot be such a penalty in the world. This endless penalty will be given to them in the next world, in Hell.