Praise be to Allah, and peace and blessings be upon the Messenger of Allah. To proceed:
Seeing Allah, the Exalted, with one's eyes in this worldly life while awake is not possible. This is established by the Qur'an and the Sunnah. When Prophet Moses (Musa), peace be upon him, asked his Lord to let him see Him, Allah said:
"You will not see Me."
It is also authentically reported that the Prophet ﷺ did not see his Lord with his physical eyes during the Night Journey and Ascension (Al-Mi'raj). When he was asked about this, he replied:
"He is Light; how could I see Him?"
As for seeing Allah in a dream, a number of scholars have stated that it is possible in general. Some of them cited reports indicating that the Prophet ﷺ saw his Lord in a dream, and it has also been narrated from some leading scholars, such as Imam Ahmad, that such a vision is possible.
However, this is not a vision of Allah's true Essence as He really is, because nothing resembles Allah. What a sleeping person sees is a vision appropriate to the nature of dreams. Therefore, dreams cannot be used as a source for Islamic rulings or matters of creed.
For this reason, Muslims should beware of those who claim that they saw Allah and then use such claims to introduce religious rulings, establish beliefs, or assert a special spiritual status. The religion is not taken from dreams; rather, it is taken from the Noble Qur'an and the authentic Sunnah.
Summary
Seeing Allah with the physical eyes in this worldly life is impossible. As for seeing Him in a dream, some scholars affirmed that it is possible in a manner appropriate to the world of dreams. However, dreams are not a source of Islamic creed or legislation, and they cannot be used as evidence for religious rulings or claims of special distinction.
And Allah knows best.