Abu Huraira (Allah be pleased with him) reported that Allah's Messenger (ﷺ) said:He who takes anyone as his ally without the consent of his previous master, there will be the curse of Allah and that of His angels upon him, and neither, any obligatory act of his nor the supererogatory one will be accepted (by Allah)
The chain is ordered from the source of the saying to the compiler: 1 = the speaker/first transmitter, the following links those who passed it on in turn, and at the bottom Muslim who compiled the work. Click a narrator to list every hadith in which he appears; the number in parentheses is how many hadiths across the collections on this site the narrator appears in.