Ibn Taymiyyah writes:

‘…The belief that supplication is more acceptable near graves has given rise to the practice of regular visits to certain graves. Urs is held at appointed days at certain graves. This practice is in contradiction to the Prophet's prohibition of not taking graves as place of gatherings. Moreover, he cursed the Jews and the Christians for having turned graves of their Messengers into places of worship. He had explicitly asked his community not to take graves as mosques, a wrong deed committed by earlier communities. Yet, Urs (procession) is held at appointed dates at several graves. People assemble there exactly in the same manner as they do at Arafat, Muzdalifah and Mina. So much attention is paid to Urs that one feels that such arrangements are not made even for Hajj. People visit these graves from far and wide, and in the same manner as for Hajj. Some people even refer to these journeys as Hajj itself.

Such a journey for making supplication or worshiping near graves cannot be held as lawful in any case. No Muslim scholar can dispute this point. Some pseudo-scholar of later date might have justified it, which is not in our knowledge. What is plainly clear is that such a practice amounts to taking graves as places of gatherings...Those indulging in innovation have even erected mosques at these grave… The pious people, no doubt, deserve our love and obedience in that they have revived the faith. We should undoubtedly follow them. We should make supplication for their forgiveness and that Allah's Mercy and Pleasure descend on them. However, we should never take their graves as places of congregation. For such practices have been forbidden by Allah and His Messenger. We must shun these.

What lies at the root of this innovation is the belief that it is better to pray near graves and that it leads to the acceptance of one's supplication. If this false belief is removed from the minds and hearts, this practice would come to an end. We consider it as our duty to reiterate the point that there are many evils in congregating near graves hence making supplications there is forbidden as is offering prayer there. However, offering supplications there is much more serious in that it poses a serious trial for the Muslim community. It opens the door to polytheism. A Muslim who is concerned about his faith and about his success in the Hereafter must avoid this innovation.'

Iqtida Sirat al-Mustaqim