Yadav, who is also the NDA convenor, said "his (Kalam's) conscience has woken up late. It is for self-aggrandisement. We used to respect him a lot but now are very saddened after such comments".
The JD(U) chief's comments against Kalam, who was made president during NDA regime, came after the former President revealed in a book that he was ready to swear in Sonia Gandhi as Prime Minister in 2004 without any hesitation even as there was intense political opposition from some quarters on the issue of her foreign origin.
In his book " Turning Points", Kalam also suggested that former Prime Minister Atal Bihari Vajpayee was not keen about his visit to Gujarat following the riots there in 2002.
Kalam's remark has given the Congress an occasion to question Vajpayee's commitment to 'Rajdharma' which the former Prime Minister is learnt to have advised Narendra Modi to follow in Gujarat.
Yadav questioned as to why Kalam remained silent for eight years even as "wild rumours and gossips" went on in the political space.
Yadav said, "constitutional head should speak out the truth when it is required. Talking of conscience when it suits you does not matter. Gandhiji used to speak according to his conscience immediately. Why did he (Kalam) kill his conscience then".
The JD(U) chief also sought to know the reason for speaking out truth eight years after the event unfolded.