It is reported of Umar  that he made the Takbeer for starting the prayer then he used it (91) as an opening supplication in his prayer.

Footnotes.
(91) The reference here is to the preceding opening supplication.

Reporters.
Reported by Muslim; however, his reported chain of ascription, Al-Albani said, is not continuous. Al-Albani said this hadeeth was of sound ascription as reported by other than Muslim. He also included this hadeeth in The Authentic of Good Sayings as #64.