Guru Nanak had changed Bhai Lehna’s name to Angad. After many tests, Guru Nanak chose Bhai Angad over his own sons to be his successor. On September 2, 1539, he told Baba Budha Ji to perform the ceremony, Guru Nanak told everyone to bow to the second master Guru Angad. 

Guru Nanak’s sons were not happy. They felt that one of them deserved to be the next Guru, but Guru Nanak told them that only Guru Angad showed the devotion to be appointed his successor. The Guru picked him because it was a position that required a humble nature and patience and only Guru Angad had displayed that throughout his service. 

We must understand one thing, Guru Nanak passed his soul on to Guru Angad Saheb: 

QwipAw lihxw jIvdy guirAweI isir CqR iPrwieAw[ 
joqI joiq imlwiekY siqgur nwnk rUp vtwieAw[ 

                                         (Vaar 1, Pauree 45 – Bhai Gurdas Ji) 

Translation: 

While still alive, Guru Nanak made Bhai Lehna the Guru. 

The two souls became one and Guru Nanak changed his body. 



After this, Guru Nanak told Guru Angad to go back to Khadoor and meditate. 

so itkw so CqR isr soeI scw qKq itkweI] 
gur nwnk hMdI mohr hQ gur AMgd dI dohI iPrweI] 
id`qw C`f krqwrpur bYT KfUry joiq jgweI] 
jMmy pUrb bIijAw ivc ivc hor kUVI cqrweI] 

                                     (Vaar 1, Pauree 46 – Bhai Gurdas Ji) 

Translation: 
With the same mark (on the forehead), the same canopy he radiated on the Throne. The power Guru Nanak had is now with Guru Angad was publically proclaimed all around. Guru Angad left Kartarpur and spread his light while sitting at Khadur. Action seeds of the previous births sprout; all other ingenuinities are false. 

Five days later, on September 7, 1539 Guru Nanak left his body.