What is the authenticity of the hadith that mentions that the Prophet, peace and blessings be upon him, ordered a prayer to be performed over a slave after the angels almost came between him and the Prophet, and he said: "Pray over whoever says 'There is no god but Allah'"?

The hadith "Pray for whoever says 'There is no god but Allah'" is very weak and unreliable through all its chains of transmission, as mentioned by several scholars, including Al-Ajlouni, Al-Albani, and Al-Munawi. As for the story of the Prophet, peace be upon him, going to Quba and his prayer over the black slave who sometimes prayed, it was narrated by Al-Khallal, Abd Al-Razzaq, Al-Tabarani, and others with similar wordings. It indicates that the Prophet, peace be upon him, prayed over him despite his inconsistency in prayer.

Al-Haythami improved the isnad (chain of narration) of Al-Tabarani, and Al-Tabarani explained the hadith by saying that the deceased's masters saw him pray sometimes, and he might pray where they did not see him, so they belittled him for that. If he had abandoned prayer completely, he would have been a disbeliever. Ibn Qudamah stated that one who abandons prayer out of negligence is prayed over and is not considered an apostate, and this is the consensus of Muslims. Ibn Abd Al-Barr mentioned the weakness of the hadiths about praying over one who says "There is no god but Allah," but that the consensus supports and validates them.