"Birthday greetings to Delhi CM Arvind Kejriwal. I pray for his long life and good health," PM Modi said in a brief tweet.
Kejriwal thanked Modi for his wishes, saying "thank u so much sir".
Last month, unleashing one of the most severe attacks on Modi, Kejriwal had said that PM may get him killed.
"He (Modi) can go to any extent and may get us killed. He may get me killed as well. Talk to your families and see if you are ready for the ultimate sacrifice," Kejriwal had told AAP volunteers, MLAs and Delhi Government Ministers.
"Modi has lost all sense of proportion and is hell bent on vanquishing the AAP," Kejriwal had said in a nearly 10-minute-long video message posted online.
Moreover, Delhi's AAP government and LG Najeeb Jung also have been locked in tussles over various issues in past.
Modi's "birthday greetings" tweet to Kejriwal and his reply were re-tweeted by several AAP leaders on Twitter.
(With PTI inputs)