According to Valmiki Ramayana, son of Laxmana, Chandraketu was given the title of "Malla" by Laxmana himself as he was master in wrestling (Malla-Yuddh).
Ramayana also says that Rama coronated his eldest son Kusa as the king of kusavati, present kushinagar which was a part of Gorakhpur district till 1946. After Ram's renunciation of the world, Kusa left Kusawati and came to Ayodhya. After him, Laxmana's two sons Angad and Chandraketu were given to rule this land of kusavati.
Angad settles with making his capital at "Angadia" and Chandraketu made "Chandrakanta" as his capital. This palce "Chandrakanta" which is current Kushinagar is mentioned as "Malla-Rashtra" AND "Malla - Bhumi" in Valmiki Ramayana after the title of Chandraketu.
Later on, the Chadraketu descendent kept the title of "Malla". By this way, the ancient Malla are Suryavanshi Ishvaku Kshtriyas with Vashisttha Gotra and ruled the present day Gorakhpur, Kusinagar.
The journey from Suryavanshi Kshtriyas to present day Sainthwar took place in last 6000 years which is very interesting.
1. History of Kosala up to the rise of the Mouryas- By vishuddhanand Pathak (Pages 197, 252)
2. PurÄ tattva, Issue 16 - By Indian Archaeological Society (page 40)
3. Journal of Indian history, Volume 57 - By University of Allahabad. Dept. of Modern Indian History, University of Kerala. Dept. of History, University (page 67)
4. Uttar Pradesh district gazetteers, Volume 48 - By Uttar Pradesh (India) (page 18)
5. Rays and ways of Indian culture - By D. P. Dubey (pages 19)
6. History of Ancient India: From 4250 BC to 637 AD - By J.P. Mittal (pages 426)
Sainthwar Kshtriyas have dedicated site as www.rajputms.co.in