Abu Hurairah reported the Prophet ﷺ as saying: if a man becomes the client of any people without the permission of his patrons (i. e. those who have freed him), on him will be the curse of Allah, of angels and of all people; no obligatory or supererogatory worship will be accepted from him.
Hadith Referenceسنن ابي داود / أبواب النوم / 5114
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:صحيح مسلم (1508)
Hadith Takhrij« صحیح مسلم/العتق 4 (1508)، الحج 85 (1371)، (تحفة الأشراف: 12376)، وقد أخرجہ: مسند احمد (2/398، 417) (صحیح) »
1؎: The restriction of «من غير إذن مواليه» is for greater censure; even if the mawali permit it, it is still forbidden for someone to take a non-mawla as his own mawla.