Dought & clear, - How was prayer first prescribed?.

I have heard that during the early years of islam, muslims were told
to perform 40 prayers a day, but this was cut down by 5 each time
ALLAH (S.W.T) knew this was unachievable by majority of muslims until
their were only 5 salat a day were left. is this because ALLAH (S.W.T)
has shown us mercy?.
Praise be to Allaah.
What you have heard about the prayer is not correct. The correct
version is that Allaah initially – on the night of the Mi'raaj when
our Prophet(peace and blessings of Allaah be upon him) was taken up
into heaven – enjoined fifty prayers to be performed night and day.
Then the Prophet(peace and blessings of Allaah be upon him) kept
asking his Lord to reduce it until it became five prayers to be
offered night and day. But Allaah decreed the reward of fifty prayers
for these five, so whoever prays five prayers will receive the reward
of fifty prayers.
It was narrated that Anas ibn Maalik said: Abu Dharr narrated that the
Messenger of Allaah(peace and blessings of Allaah be upon him) said:
"The roof of my house was split open when I was in Makkah, and
Jibreel(peace and blessings of Allaah be upon him) came down and split
open my chest and washed it with Zamzam water. Then he brought a
golden vessel filled with wisdom and faith and poured it into my
chest, then he sealed it. Then he took me by the hand and ascended
with me into the lowest heaven. When I reached the lowest heaven
Jibreel said to the gatekeeper, 'Open up!' He said, 'Who is this?' He
said, 'Jibreel.' He said, 'Is there anyone with you?' He said, 'Yes,
Muhammad(peace and blessings of Allaah be upon him) is with me.' He
said, 'Has his mission begun?' He said, 'Yes.' And when it was opened
we went up into the lowest heaven… Then Allaah enjoined upon my ummah
fifty prayers, and I came back until I passed by Moosa who said, 'What
has Allaah enjoined upon your ummah?' I said, 'He has enjoined fifty
prayers.' He said, 'Go back to your Lord, for your ummah will not be
able to bear that.' So I went back and He reduced it. Then I came back
to Moosa and said, 'He has reduced it.' He said, 'Go back to your
Lord, for your ummah will not be able to bear that.' So I went back
and He reduced it further. Then I came back to Moosa and said, 'He has
reduced it further.' He said, 'Go back to your Lord, for your ummah
will not be able to bear that.' So I went back and He said, '(The
prayers) are five but (the reward) is fifty. The Sentence that comes
from Me cannot be changed [cf. Qaaf 50:29].' Then I went back to Moosa
and he said, 'Go back to your Lord.' But I said, 'I feel shy before my
Lord.'…"
Narrated by al-Bukhaari, 342; Muslim, 163
Al-Haafiz Ibn Hajar said:
What is meant is that they are five with regard to what is to be done,
but they are fifty with regard to the reward.
Fath al-Baari, 1/463
And Allaah knows best.