Lutifullah Mashal, a spokesman for the Afghan intelligence service, says the plot originated near Quetta.
Mashal told reporters on Saturday that investigators provided addresses, photos and maps to the Pakistani embassy in Kabul.
Rabbani was trying to broker peace with the Taliban when he was killed by a suicide bomber.
At the UN last week, Afghan officials said the killing was plotted for four months by the Afghan Taliban’s governing council, the Quetta Shura.
The Taliban have not claimed responsibility for Rabbani’s death.