Midrash su Ecclesiaste 3:7

36) (Vayikra 10:3): "And Moses said to Aaron: This is what the L–rd spoke, saying: With My near ones will I be sanctified, and before all the people will I be slaughtered. And Aaron kept his peace." This (in essence) was spoken to Moses on Sinai, and he did not know it (i.e., its intent) until what it spoke of (the deaths of Nadav and Avihu) materialized before him. And when it came to pass Moses said to Aaron: Aaron, my brother, your sons died only to sanctify the Name of the Holy One Blessed be He, as it is written (Shemoth 29:43): "And I shall be appointed there (in the tent of meeting), and it will be sanctified with My glory," (the death of Aaron's sons there, intensifying its awe in the eyes of the people). When Aaron saw how exalted were his sons in the eyes of the L–rd, he kept his peace and was rewarded for doing so, (by G d's addressing to him exclusively the following section [viz. Shemoth 10:8-11]). From here it was derived: All who accept (G d's decrees) upon themselves and remain silent — it is an auspicious sign for them. As expressed by David (Tehillim 37:7): "Be silent in the L–rd, and hope to Him." And, as expressed by Solomon (Koheleth 3:7): "a time to be silent and a time to speak." There are times for all (things). There are times when a man remains silent, and there are times when a man speaks.