Numbers 12:4

(4) And the LORD spoke suddenly unto Moses, and unto Aaron, and unto Miriam: ‘Come out ye three unto the tent of meeting.’ And they three came out.

Now Moses was not with them, but [they are mentioned together because] the Divine communication came to the three of them simultaneously. The sense of the word “suddenly” is that they did not direct their minds towards or intend to receive a Divine communication at that time, it being in honor of Moses that it came to them without any preparation for it; for the word pith’om (suddenly) in the opinion of the commentators [as explained in Ibn Ezra] applies to something which one did not think of, from the root pethi (simple-minded). Therefore Scripture uses the term pith’om [only] on account of Aaron and Miriam, for Moses our teacher was fit for a Divine communication at any time, and his mind was prepared to cleave to the Glorious Name at every moment, as our Rabbis have explained in connection with the reason why he [Moses] separated himself from his wife...

(4) And the LORD spoke in a hurry to Moses and to Aaron and to Miriam "Come forth, you three, to the tabernacle of ordinance." And the three went forth.

Peresh Rashi – He revealed Himself to them suddenly, when they were ritually unclean following marital relations, and they cried, "Water, water!" [They needed water to purify themselves.] He thus showed them that Moses had done right in separating from his wife, since the Divine Presence revealed itself to him frequently, and there was no set time for Divine communication.

And there are some that interpret פתאם so that they will not be able to do t'shuvah, because in their words this is a matter of desecrating God - that any who speaks disparagingly of the prophets it is as if they speak against the Shechina...

ויאמר ה' פתאם.

and we clarified in Exodus 4:3 that because of the miracle in front of the snake [when he ran away] while he was standing before God, and because he was suddenly frightened until [the point that] he did not realize in front of whom he was standing; for some reason פתאם comes here for the sake of a punishment, that he was spoken to suddenly.