Ibn Ezra

"and He said" - according to my opinion, this passage is attached to one that precedes it, for the firmament was not made until the earth became dry, and as proof: "On the day which Hashem, G-d, make earth and heaven" - behold, on one day they were made. Now revealing a hidden thing and gathering that which is scattered is not creation [per se] (beri'ah). The meaning is then, "G-d had already said, let the waters be gathered", and there are hundreds of similar usages in the Torah. In parashat Bereshit alone I will give you two witnesses. The first: "And He placed there [in the Garden] the man whom He had formed", while afterwards, "And Hashem, G-d, caused to grow [from the ground every tree...]" - but before [placing] man had He caused it to grow. The second witness: He commanded man not to eat from the tree of knowledge, and afterwards it is written, "And Hashem, G-d, formed from the ground..." - rather, its explanation is, "He had already formed". According to this explanation, the words, "and G-d saw that it was good" [verse 10] refers to the second day, and "Let the earth bring forth grass" is the beginning of the third day. The explanation of "let them be gathered" is: "let them join together", and likewise: "[and all the nations] shall be gathered to her [Jerusalem] Jeremiah 3:17