Mahadev leads the Maha Mantra: Hare Krishna Hare Rama kirtan chanting during a satsang at Yoga Vidya in Bad Meinberg, Germany. To sing along you can find the maha mantra in the Yoga Vidya Kirtan Songbook as number 2. Things to know about the Maha Mantra can be found in German in the Yoga Wiki: Mahamantra.