Allamah Majlisi narrates in volume 2 of Hayatul Qoloob,
under the chapter of Meraj of Prophet (s.a.w.a.) that on the
night of Meraj the Holy Prophet (s.a.w.a.) saw some beautiful
palaces in paradise. However he observed that these beautiful
palaces were dark and unlit. He (s.a.w.a.) asked Jibrael the
reason for the same. He replied that these palaces belong to
those believers who are regular in namaz and fasting but they
are negligent and lazy in reciting salawaat after namaz. Hence
these palaces are bereft of illumination. Even if they, starting
today, commence the recitation of salawaat then these palaces
will be lit once again
Ref : Fazila e Salawaat