Rashi on Numbers 11:30/רש"י על במדבר י״א:ל׳

1ויאסף משה AND MOSES [AND THE ELDERS OF ISRAEL] RETIRED from the entrance of the appointed tent.

2אל המחנה INTO THE CAMP — i.e. they each went into his tent in the camp. ...

3אסף — ויאסף is a term for “bringing into the house”, as, (Deuteronomy 22:2) “thou shalt bring it (ואספתו) into thine house”, The passage that proves that this is so in all cases (lit., the father of all) is, (Psalms 39:7) “he heapeth up riches, and knoweth not who shall gather them in (אוספם)” (from which it is evident that אסף must denote not “gathering together” for this is implied in יצבר, but bringing it into one’s house, taking possession of a thing). The fact that Scripture first relates that Moses and the elders entered their tents and afterwards that punishment fell upon the people teaches us that He (God) did not bring the punishment upon them before these righteous men had retired each into his tent (Sifrei Bamidbar 96).