Praise be to Allah.
We put this question to Shaykh Muhammad ibn Saalih al-‘Uthaymeen, may Allaah preserve him, who answered as follows:
What they get (i.e., payments) without asking for it will not detract from their reward.
The people who made this web-site say in one part of their site that anyone who wants to place an advertisement with us on a monthly basis has to pay a certain amount, in return for which they will place the advertisements.
If that is the case, then this money will detract from their reward, because they are the ones who are asking for it. But if they take what is given to them to help them with what they are doing, there is nothing wrong with them taking it. It says in the hadeeth of ‘Umar that the Prophet (peace and blessings of Allaah be upon him) said: “If any of this money comes to you without your hoping for it or asking for it, then take it, and whatever does not come to you, do not trouble yourself about it (i.e., if it does not come to you, do not seek it, leave it alone).”
(Narrated by al-Bukhaari, 1473)
And Allaah knows best.