Sajjan kept a serai on the road near Tulamba with a mosque on one side and a temple on the other, so that travellers of either religion would stop. He murdered them in the night and took their goods.
Guru Nanak Dev Ji and Bhai Mardana Ji stayed. Instead of sleeping they sang, and the hymn they sang, in raga Suhi, says that bronze shines brightly and rubbing it leaves a black stain, and that washing it a hundred times will not remove it.
The account says Sajjan understood that he had been described, confessed, and was told to give back what he had taken and to feed travellers instead of killing them.
The first Sikh dharamsala is said to have been established at that spot.
It is the most-told story in the janamsakhi corpus about the possibility of change, and the mechanism in it is a song rather than a punishment.
The name Sajjan means friend or good man, and the janamsakhi is using it against him. English retellings call him a thug, which takes a nineteenth century colonial category out of the suppression campaigns of the 1830s and puts it on a Punjabi text written long before, which does not use the word at all.
The confrontation is verbal. The hymn sung at him compares a whitewashed house to a heron, white outside and eating fish, and he confesses on hearing it.
Tulamba is in Khanewal district in Pakistan and a shrine is associated with the episode. The story is the standard example in the tradition of religious display used as cover.