Allah Said to Moosa (peace be upon him): “O Moosa, I did not grant that to Myself so how could I grant it to you?”

We could not find this report with any reliable isnad (chain
of transmission), and we did not find it in the books of Sunnah (prophetic
teachings) and reports. Rather we saw it in some books of raqaiq (heart
softening reports) and exhortation, without mentioning any isnad or reliable
source.  

Ibn Muflih al-Maqdisi (may Allah have mercy on him) said:

“Moosa (peace be upon him) said: ‘O Lord, the people are
saying things about me that are not true.’ And Allah revealed to him: ‘O
Moosa, I have not granted that to Myself, so how could I grant it to you?’”
End quote. 

Al-Adab al-Shar‘iyyah, 1/7-8; there is a similar report in
Qoot al-Quloob by Abu Talib al-Makki, 2/309; Siraj al-Mulook by Abu Bakr
al-Tartooshi (229).  

Although we cannot prove it because we could not find any
isnad for it, there does not appear to be anything wrong with its meaning,
because Allah did not decree — in any of the universal natural laws that He
decreed — that none of His creation would overstep the mark towards Him or
that any human could ever deal with their Lord in a way that is not
befitting to His Majesty and Might; rather He has told us of people who fell
short in this regard and did not estimate Him with an estimation due to Him,
as He says (interpretation of the meaning):

“They (the Jews, Quraysh pagans, idolaters) did not estimate
Allah with an estimation due to Him when they said: ‘Nothing did Allah send
down to any human being (by Revelation).’ Say (O Muhammad – peace and
blessings of Allah be upon him): “Who then sent down the Book which Moosa
(Moses) brought, a light and a guidance to mankind which you (the Jews) have
made into (separate) paper sheets, disclosing (some of it) and concealing
(much). And you (believers in Allah and His Messenger Muhammad (peace and
blessings of Allah be upon him) were taught (through the Quran) that which
neither you nor your fathers knew.” Say: “Allah (sent it down).” Then leave
them to play in their vain discussions.”

[al-An‘am 6:91] 

“They have not estimated Allah His Rightful Estimate. Verily,
Allah is All‑Strong, All‑Mighty.”

[al-Hajj 22:74] 

“They made not a just estimate of Allah such as is due to
Him. And on the Day of Resurrection the whole of the earth will be grasped
by His Hand and the heavens will be rolled up in His Right Hand. Glorified
be He, and High be He above all that they associate as partners with Him!”

[al-Zumar 39:67]. 

The Prophet (peace and blessings of Allah be upon him) said:
“No one is more patient in bearing offensive things that he hears than
Allah, may He be glorified and exalted; others are associated with Him, a
son is attributed to Him, but He still grants them health and provision.”
Narrated by al-Bukhari (7378) and Muslim (2804). 

What we learn from this is that the criticism of the envious
and the slander of those with ulterior motives is not a reason for a Muslim
to be discouraged from trying hard to succeed and progress, or to weaken his
resolve or cause him to become frustrated. He should always remember that
Allah, may He be glorified and exalted, the Angels, the Messengers and the
Prophets were never safe from slander and harm. 

And Allah knows best.