Bhai Gurdas, Varan, 1.38, states that, in Guru Nanak`s time, Sodaru and Aratl were sung in the evening while Japu was recited in the early hours of the morning. Then, evidendy, the first and the second hymns only of the present text were called Sohila, while the third hymn, also of Guru Nanak, was called Aratlas it has been so captioned in the Guru Granth Sahib. These two were treated as distinct bams.
Guru Arjan added two more hymns and entered all the five in the Guru Granth Sahib in 1604 as one ban! under the title of Sohila. Later, more exactly and authoritatively, this barn was prescribed as the bedtime prayer when, in 1699, Guru Gobind Singh inaugurated the Khalsa administering to it the vows of amrit and laying down for it a specific code. Legend has grown, that if one goes to bed after reciting the Sohila, one`s
References :
2. Amole, S.S., Kirtan Sohila. Amritsar, 1945