Authentic Supplication Number 105.

After having ended his salat the Messenger of Allah  used to ask for forgiveness three times [for example: ‘Astaghfirullaha  ], then he would say Allahumma ‘antas-salamu (123), wa minkas-salamu, tabarakta ya thaljalali wal ‘ikrami (124).

(123) As-Salamu is Allah. Al-Qurtubee said that As-Salamu means the one that is free from flaws. Ibn Al-‘Arabi said: The scholars, may Allah have mercy upon them, have agreed that the meaning of As-Salam is the attribution of Salamata to Allah which means to be safe, and to be free from vice and defect. The scholars then differed in how they attributed Salamata to Allah, they were of three opinions. The first that Allah is free from every defect and flaw. The second that Allah is the one that conveys peace upon his worshippers in paradise as in the verse  (Salamun: a statement from a merciful Lord). The third meaning is that his creation has been kept safe and free of injustice on his part. As-Salam is also explained to mean that Allah is the one that keeps those of his creation whom He wills safe. This explanation was translated from ‘Aqd ‘Azzabarjad fee Tahiyyat ‘Ummat Muhammad which was written by As’ad ‘ Al-‘Usaymee.

(124) O’ my ‘ilah You are ‘As-Salam [see footnote #123], and from You comes Salam [peace, or safety], blessed are Thee O’ haver of glory and kindness.

Reported by Muslim, and Al-Albani included this hadeeth in The Authentic of Good Sayings.