This quotation appears to come from the prologue of Aeschylus' Agamemnon, which was first staged in 458 BCE. The words are spoken by the Watchman, who has been perched on the roof of Agamemnon's house and has been waiting for a signal that Troy has been conquered and that Agamemnon is returning home from Troy.
At the end of this prologue speech, the Watchman, who is addressing the audience, seems to be on the verge of commenting upon the horrific events that have happened in the past to Agamemnon's ancestors.
But this house,
if it could speak, might tell some stories.
I speak to those who know about these things.
For those who don't, there's nothing I remember.
(Ian Johnston translation)
Not only have Agamemon's ancestors been involved in horrific events, but while Agamemon has been away at Troy, his wife has been having an affair with Aegisthus and the two have been plotting to kill Agamemnon upon his return from Troy. The Watchman seems to know about all of the terrible things that have happened in the house, but as he ends his prologue he tells the audience that he will remain silent about these things.