Who was first to show that the first nine of the ten plagues could be grouped into three groups of three?

Question

Who was first to show that the first nine of the ten plagues could be grouped into three groups of three?

1. The First Plague: Water Turned to Blood דָּם (7:17-24; 7:17-24) Go to Pharoah – לֵ֣ךְ אֶל־פַּרְעֹ֞ה

2. The Second Plague: Frogs צְפַרְדֵּעַ (7:25-11; 7:25-15) Go to Pharaoh – בֹּ֖א אֶל־פַּרְעֹ֑ה

3. The Third Plague: Gnats/Lice כֵּן (8:12-15; 8:16-19) No pre-announcement to Pharaoh – The magicians … they could not. הַחַרְטֻמִּ֧ים ...‬ וְלֹ֣א יָכֹ֑לוּ – This is the finger of God! – אֶצְבַּ֥ע אֱלֹהִ֖ים הִ֑וא

4. The Fourth Plague: Flies/Insects עָרֹב (8:16-28; 8:20-32) present yourself to Pharaoh – וְהִתְיַצֵּב֙ לִפְנֵ֣י פַרְעֹ֔ה

5. The Fifth Plague: Egyptian Livestock Die בָּקָר (9:1-7; 9:1-7) – Go to Pharaoh – בֹּ֖א אֶל־פַּרְעֹ֑ה

6. The Sixth Plague: Boils שְׁחִין (9:8-12; 9:8-12) No pre-announcement to Pharaoh – magicians were unable – וְלֹֽא־יָכְל֣וּ הַֽחַרְטֻמִּ֗ים

7. The Seventh Plague: Hail בָּרָ֖ד (9:13-35; 9:13-35) present yourself to Pharaoh – וְהִתְיַצֵּ֖ב לִפְנֵ֣י פַרְעֹ֑ה

8. The Eighth Plague: Locusts אַרְבֶּ֖ה (10:1-20; 10:1-20) – Go to Pharaoh - בֹּ֖א אֶל־פַּרְעֹ֑ה

9. The Ninth Plague: Darkness חֹ֖שֶׁךְ (10:21-29; 10:21-29) No pre-announcement to Pharaoh

10. A Final Plague בְּכֹור֮ I will not see your face again. – לֹא־אֹסִ֥ף עֹ֖וד רְאֹ֥ות פָּנֶֽיךָ

Answer 1

According to many commentators (esp. Maharal), this was the intent of Rabbi Yehudah when he broke the plagues into three groups in his mnemonic:

רַבִּי יְהוּדָה הָיָה נוֹתֵן בָּהֶם סִמָּנִים: דְּצַ"ךְ עַדַ"שׁ בְּאַחַ"ב.
Rabbi Yehuda was accustomed to giving [the plagues] mnemonics: Detsakh [the Hebrew initials of the first three plagues], Adash [the Hebrew initials of the second three plagues], Beachav [the Hebrew initials of the last four plagues].

The last plague stands on its own after the three sets of three (Maharal ad loc.), so it gets tacked onto the end of the last set.