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Gulati, Mahinder N. (2008). Comparative Religious And Philosophies: Anthropomorphlsm And Divinity. Atlantic Publishers. pp.316–319. ISBN 978-81-269-0902-5.
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Ménage, V. L. (1979). "The "Gurū Nānak" Inscription at Baghdad". Journal of the Royal Asiatic Society of Great Britain and Ireland. Cambridge. 111 (1): 16–21. doi: 10.1017/S0035869X00134999. JSTOR 25210997. S2CID 163324791. a b c Pashaura Singh; Louis E. Fenech (2014). The Oxford Handbook of Sikh Studies. Oxford University Press. pp.127–129. ISBN 978-0-19-969930-8. Kaur, Nikky-Guninder Singh (2004). Sundararajan, K. R. (ed.). Hindu Spirituality: Postclassical and Modern. Motilal Banarsidass. p.530. ISBN 81-208-1937-3.
Bhai Banno (right) being given the Adi Granth by Guru Arjan (centre-left) to get it boundThe third view held by scholars such as Piar Singh states that independent versions of the Sikh scripture developed in geographically distant regions of the Indian subcontinent.  These versions developed because of the forgetfulness or creativity of the local Sikh leaders, errors made by scribes, attempts to adopt popular hymns of bhagats or adapt the hymns to local regional languages where Gurmukhi was not understood. It is these manuscripts that Guru Arjan collected and considered, then edited to produce an approved version of the Adi Granth. The Sikh scripture, according to this school, was thus a collaborative effort and there was no authentic version of the pre-canonical text in Sikhism. 
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a b c Pashaura Singh; Louis E. Fenech (2014). The Oxford Handbook of Sikh Studies. Oxford University Press. pp.129–130. ISBN 978-0-19-969930-8.Singh, Kamalroop. "Sikh Martial Art (Gatkā)." The Oxford Handbook of Sikh Studies. Oxford University Press, 2014. 459. Gurpurnali written in 1727 and Guru Tegh Bahadur Malwe da Safar written in 1716 both mention Guru Nanank being born on the full moon of Katak.