And it came about, while Israel was living in that land, that Reuben went and slept with his father’s concubine Bilhah, and Israel heard about it. Genesis 35:22 (NASB)
Jacob, now called Israel, suffers grief beyond measure in this chapter. His beloved wife has just died. Shortly, his father will die. Presumably, his mother has died as well, along with his mother's nurse.
In the middle of this narrative of loss, Israel's eldest son, Ruben, takes the opportunity to sleep with Bilhah, Jacob's concubine. But Bilhah is more than just Israel's concubine. Bilhah is Rachel's servant.
The text says that "Israel heard about it." From whom? And why does he remain silent now? Perhaps this is the emptiness of grief. But perhaps the writers are showing us something about the responsibility (and failure) of the firstborn son.