The application of henna to the hands as a form of decoration is known as Mehndi and is commonly applied during weddings or festivals in South Asia. It is thought to have originated in India as a ceremonial art form, with Mehndi being applied to a bride's hands and feet prior to the marriage ceremony.
The Vedas are the oldest Hindu scriptures. Each veda contains thousands of hymns, some of which are thought to be 6000-8000 years old. In the video below you can hear a mantra from the Yajurveda being chanted.