Wala tusalli AAala ahadin minhum mata abadan wala taqum AAala qabrihi innahum (surah Tawbah: 84)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(9:84) And in future you should never say funeral prayer for anyone from among them; who dies nor stand at his grave, for they have denied Allah and His Messenger and died the while they were transgressors. *88

Wa laa tusalli `alaaa ahadim minhum maata abadanw wa laa taqum `alaa qabriheee innahum kafaroo billaahi wa Rasoolihee wa maatoo wa hum faasiqoon

*88) This verse was sent down to prevent the Holy Prophet from saying funeral prayers for 'Abdullah bin Ubayy, the ringleader of the hypocrites, who died a short while after the Tabuk Expedition. His son 'Abdullah who was a sincere Muslim called on the Holy Prophet and requested him to give his shirt for his father's shroud. The Holy Prophet very generously granted his request. Then he begged the Holy Prophet to lead his father's funeral prayer. The Holy Prophet agreed to this also but Hadrat 'Umar very respectfully requested him repeatedly not to do so, saying, "O Prophet of AIIah! will you say funeral prayer for a person who was guilty of such and such crimes and sins"? The Holy Prophet, who was a blessing both for friends and for foes, got ready to say funeral prayer even for that man who was a deadly enemy of Islam. At ast when he stood up to lead the funeral prayer, this verse was sent down to prevent him from this by a direct Command from God, in accordance with the changed policy declared in v. 73 which forbade to do anything that might encourage the hypocrites among the Muslims.
The above incident led to the formulation of the regulation that the leaders and prominent people from among the Muslims should neither lead nor offer the funeral prayers of the sinners against Islam or for those notorious for their disobedience to Islam. After this, whenever a request was made to the Holy Prophet for a funeral prayer, he would first enquire about the conduct of the deceased person. If he came to know that he was a bad person, he would say to Iris people, "You may perform his burial just as you like".