"When Nitish Kumar, leading the NDA registered landslide win in Bihar Assembly polls in 2010 securing 206 seats out of total 243 marking 86 per cent of the seats Narendra Modi had not congratulated him," the sources said on condition of anonymity.
"Modi had not congratulated Kumar either directly or indirectly," they said.
Kumar's silence has triggered speculation whether it was deliberate and another instance of 'unfriendly' relationship between the two NDA strongmen.
When Kumar's reaction was sought by mediamen yesterday morning on the hat-trick by Modi, he did not respond.
Kumar had not entertained similar question on December 20 evening too after the results were announced.
The silence maintained by Kumar has obviously not gone down well with BJP state leaders.
State BJP President C P Thakur had wondered why Kumar did not make the customary gesture of congratulating (Modi) which is common in public life.
Modi's supporter and state Animal Husbandry Minister Giriraj Singh said, "It is a routine practice that even a defeated candidate congratulates the winner in an election." Kumar's aversion to Modi for the 2002 Gujarat riots is well known.
Recently in an interview to a national daily Kumar had said NDA's prime ministerial choice should have secular credentials, which was construed as his opposition to the candidature of the Gujarat strongman.
On Kumar's insistence, BJP kept Modi away from the campaign in Bihar both in the 2009 general elections and state Assembly polls in 2010.
During BJP's national executive meeting at Patna in 2010, angry over publication of advertisement in newspapers about donation provided by Modi for Kosi flood victims, Kumar had cancelled a dinner he had to host for BJP leaders.