Although this day is not a part of Diwali festival, I choose to write about it’s importance because it is a special day with lot of significance. It is a very important day for the followers of Lord Dattatreya. The first incarnation of lord Dattatreya is Sreepada Sreevallabha. His birth place is Pithapuram in East Godavari district of Andhra Pradesh. He reached Kuravapur (kurugadda) which is nearer to Raichur of Karnataka, India, which is on the bank of Krishna River and performed penance there.
He concluded his avathara (incarnation) of Sreepadavallabha in Krishna river on the day of ” ASHWEEJA BAHULA DWADASHI ” and the day is termed as ” GURU DWADASHI ” in all the kshetras of Lord Dattatreya. The day is highly powerful and performing abhishekas and pujas to Lord Dattatreya in all Datta kshetras (holy places where Lord Dattatreya himself or his incarnations had resided). This year the day is falling on 27th October.
(source: http://www.indiadivine.org/content/topic/1578296-guru-dwadashi/)
A Bit of Wisdom & A Bit of Play! 
Thanks for the Knowledge. May Lord Dattatreya defeat all the Evil People.
Jai Guru Dev Datta!
Jai.
DIGAMBARA DIGAMBARA SHREEPAD VALLABHA DIGAMBARA