 भगीरथात्ककुत्स्थस्तु काकुत्स्था येन विश्रुताः।ककुत्स्थस्य च पुत्रोऽभूद्रघुर्येन च राघवाः।। 
 To Bhagiratha was born Kakutstha, by whom your race is wellknown. A son Raghu was born to Kakutstha and hence all of you are known as Raghavas. 