"On victory of grand secular alliance crackers will not be burst not in Pakistan, but in India and maximum of it in Amritsar and Mumbai," Kumar said addressing an election rally at Bahera in Darbhanga district.
The BJP's relations with National Democratic Alliance partners Shiromani Akali Dal in Punjab and the Shiv Sena in Maharashtra have been dogged by differences from time to time.
Kumar's rejoinder followed Amit Shah's assertion last week that if the BJP loses by any chance in Bihar firecrackers would be burst in Pakistan.
He alleged that Shah's assertion was aimed at "polarisation of votes on religious grounds". "The sinister plan (to polarise voters on religious line) will not succeed)."
Kumar, who is the chief ministerial candidate of the grand alliance, also hit back at his bete noire Prime Minister Narendra Modi for scoffing at his meeting a 'tantrik' and referred to the prime minister's allegedly meeting an astrologer Bejan Daruwala.
"I met an aughad (occultist) without hiding from anybody in daylight ... But news reports showed Narendra Modi allegedly meeting astrologer Bejan Daruwala.
"You are talking a lot about jantar-mantar against me but what about meeting astrologer Bejan Daruwala ... Isn't it an example of double standards?" Kumar, who is the star campaigner for the grand alliance, said.
He also tore into the prime minister's jibe at him over one of his ministers being caught on camera accepting money. Apparently referring to Union minister of state Giriraj Singh, Kumar asked, "Why was a person from whose home Rs two crore unaccounted money was found rewarded and made a minister?"
Slamming Modi for the skyrocketing prices of pulses with arhar dal costing more than Rs 200 a kg, Kumar said, "Earlier people used to chant 'Har har Modi' and now they chant 'Arhar Modi'... People are saying forget 'Achche din' (BJP's pre-Lok Sabha slogan) and return our 'Purane din' (old days)."
He invoked socialist leader Ram Manohar Lohia saying he had in 1967 said that people who are part of the government should not speak more and instead allow their work to speak.
"I follow this dictum. But what about the person who instead of fulfilling his promises on black money, special status to Bihar and enhanced MSP to farmers is only moving his lips," Kumar said in a veiled dig at the prime minister.