It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When my Companions are mentioned, hold back (from criticism); when the stars are mentioned, hold back (from debate); and when divine decree (qadar) is mentioned, hold back (from debate)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10410