Comentario sobre Exodo 7:25

וימלא AND THERE WAS COMPLETED (the verb is singular) שבעת ימים the number of SEVEN DAYS during which the river did not return to its original condition. For each plague functioned a quarter of a month and for three quarters He warned and cautioned them (Midrash Tanchuma, Vaera 13; Exodus Rabbah 9:12).

And seven days were fulfilled after that the Eternal had smitten the river.¹³⁰Verse 25. This is connected with the verse above, and the purport thereof is as follows: And with this¹³¹The verse states, ‘Vayimalei’ (And it was fulfilled) seven days, using a singular verb when the verb actually required is a plural: vayimal’u (and they were fulfilled). Rashi explained it by adding the word minyan (number) in the singular, explaining it thus: “and the number of seven days was fulfilled.” Ramban suggests that the verse is connected to the preceding one and is to be understood with the additional word of bazeh (with this), thus rendering the sense of the verse: “and with this activity — i.e., with the Egyptians’ digging, etc., as stated in the above Verse 24 — was filled (or completed) seven days.” — namely, the Egyptians’ digging round about the river for they could not drink of the water of the river, [as stated in Verse 24] — with this was filled the seven days after the river had been smitten.

שבעת ימים, this was the duration of the plague that struck the river.