As-Sabur does not appear as this exact noun applied to Allah anywhere in the Qur’an or in a hadith with a strong chain. It is widely printed in popular lists of the 99 (via the Tirmidhi enumeration), and its meaning — that Allah delays the punishment of the disobedient out of patience — is well supported by the Qur’an’s repeated descriptions of Him as Halim (Most Forbearing) and Ghafur (Forgiving), even though this precise wording is not found describing Him directly in an ayah.
As-Sabur's patience with His disobedient servants is beyond measure, giving time for return rather than immediate punishment — though, like Ar-Rashid, this specific wording rests on a weaker textual basis than most of the 99.