One Who abandons Prayer must be advised

Question :

In the past I stayed in a hospital and two persons entered the room in which I was staying and we remained there for three days. During this time I used to pray, but they did not pray even though they were Muslims from my country, and I did not say anything to them. Am I guilty of sin for not ordering them to pray, and if so what is the atonement for it? May Allah reward you with goodness.

Answer:

It was an obligation upon you to advise them and to rebuke them for the great sin which they committed, which was abandoning prayer, based upon the Words of Allah, the Most Glorified:
Let there arise out of you a group of people inviting to all that is good (Islam), enjoining Al-Ma'ruf (i.e. Islamic monotheism and all that Islam orders one to do) and forbidding Al-Munkar (polytheism, disbelief and all that Islam has forbidden). And it is they who are successful.
And other Verses which carry the same meaning, and upon the words of the Prophet :
"If any of you saw something detestable, he should change it with his hand; and if he is unable to do this, then by his words, and if he is unable to do this, then in his heart - and this is the weakest kind of faith.!

Since you did not do this, it is incumbent upon you to repent sincerely of this act of disobedience and this entails regretting what you have done, refraining from it and making the firm intention not to repeat it, in sincerity to Allah and in glorification of Him, hoping for His reward and fearing His punishment. And whoever turns to Allah in repentance, Allah turns to him in forgiveness, according to the Words of Him, the Almighty, the All-Powerful:

And verily, I am indeed Forgiving to him who repents, believes (in My Oneness and associates none in worship with Me) and does righteous good deeds and then remains constant in doing them (until his death).

Source:
Ibn Baz
Fatawa Islamiyah, Vol. 2 Pages 377-378