Vayeshev 

וישב

The brothers did not reveal the truth about Joseph to Jacob. According to the Sages, they forbade anyone, with a severe oath, to reveal it to him; therefore, even God did not reveal the sale of Joseph to Jacob. 

The brothers said: Let us impose a decree of excommunication upon ourselves ensuring that none of us will tell this matter to Jacob. Judah said to them: Reuben is not here – excommunication cannot be enacted with only nine people present. What did they do? They included the Omnipresent with them and they enacted the excommunication. They told Reuben that they enacted the excommunication, and he heard the excommunication and was silent, and the Holy One, blessed be He, too was included…. The verse states concerning God: “He tells His matters to Jacob” (Psalms 147:19), but He did not tell Jacob of this matter due to the decree of excommunication. <source>(Yalkut Shimoni, Vayeshev 1:142) </source>