From Sahih Muslim (Hadith 4183):
Nu'man b. Bashir, reported that Allah's Messenger (ﷺ) had said:Have you, besides him, other sons? He said: Yes. Thereupon he (the Holy Prophet) said: Have you given gifts to all of them like this (as you have given to Nu'man)? He said: No. Thereupon he (the Holy Prophet) said: I cannot bear witness to an injustice
Reference: Muslim 4183