Sforno on Numbers 20:3/ספורנו על במדבר כ׳:ג׳

1וירב העם עם משה, the subject of the quarrel was why Moses had brought the people to such a desert as the one they found themselves in at the time. However, there was also a complaint against G’d Himself, as the Torah testifies in verse 13 where the Torah writes: אשר רבו בני ישראל את ה', “in that the Children of Israel quarreled with G’d.” This referred to the words (verse 5) “why did you take us out of Egypt?”