The quality of political discourse in the country has hit a rock bottom and former Prime Minister Manmohan Singh urged his successor Narendra Modi on Monday to exercise "due restrain" in public speech.Singh was grilled during the launch of Manish Tewari's book "Fables of Fractured Times" to comment on the new pitfalls in the language used by politicians across party lines."My advise to the Prime Minister is to exercise due restrain that is becoming of a Prime Minister. When the PM goes to states that are not ruled by the BJP, he has an obligation to not use the language that has now become common practise," he said.Singh said that he and his Congress-led UPA government never discriminated in the fashion that the Modi dispensation is carrying out on a daily basis."We never discriminated against the BJP ruled states. (Madhya Pradesh Chief Minister) Shivraj Singhji would himself testify to this. We paid the respect that was deserving," he said.He urged Modi to set an example."He is the Prime Minister of all Indians. His conduct must be worthy and consistent with the obligation he has as a PM," Singh said at the launch of the book from Konark Publishers.