Mussar sobre Êxodo 17:8

And (Shemoth 17:1): "And they journeyed … and they encamped in Refidim," after which it is written (Ibid. 8): "And Amalek came." This is expounded by Chazal as: [Amalek attacked them] because their hand "weakened" ["rafu yedeihem" (like "refidim")] in Torah.

(Ibid. 17:7): "And he called the name of the place Massah and Merivah because of the "quarrel" (riv) of the children of Israel and because of their "proving" (nasotham) the L-rd, saying: 'Is the L-rd in our midst or not?'" This is followed by (8): "And Amalek came and warred, etc." From the juxtaposition of the verses we learn that the sin of Merivah also contributed to bringing Amalek upon them. The same holds true for other idolatries — wherefore one must take great care to avoid merivah (quarreling).