It is narrated in books that when the Holy Prophet (s.a.w.a.)
travelled to the skies in the night of Meraj, on the fourth
heaven he met an angle who had a tablet with him and was
looking at it very closely. He kept on looking at it with
amazement. His eyes were filled with tears and therefore he
did not see the Holy Prophet (s.a.w.a.) and stand out of respect
for him.
He awoke from his reverie by the sound of the flapping of
wings of Hazrat Jibrael; he kissed the reins of the steed of Holy
Prophet (s.a.w.a.) and sought forgiveness from him. The
Prophet (s.a.w.a.) asked him what was written on the tablet. He
replied, O Prophet (s.a.w.a.) it is written on this tablet – La
Ilaha Illallah. Mohammadun Rasoolallah. Aliyun Waliullah.
He then said, O Prophet (s.a.w.a.), I recited a 2 rakat namaz by
the order of Allah for 20,000 years. I recited it in such a
manner that for 5,000 years I stood in namaz, 5,000 years I was
in the condition of ruku, 5,000 years in sajdah and 5,000 years
I recited tashahhud. I gifted the reward of this namaz to you O
Prophet of Allah (s.a.w.a.). As a reward for this, please
overlook my mistake (of not standing in your respect.) The
prophet said, I do not need your obedience. The angle said, I gift this to your Ummah. The prophet (s.a.w.a.) replied, my
Ummah also is not in need. I swear by Allah if a sinful person
from my Ummah recites salawaat upon me, the reward of that
is better than your namaz of 20,000 years
Ref : Fazila e Salawaat