Saṃyutta Nikāya 46
Connected Discourses on the Factors of Enlightenment
50. External Factor
“Bhikkhus, as to external factors, I do not see any other factor that is so helpful for the arising of the seven factors of enlightenment as this: good friendship. When a bhikkhu has a good friend, it is to be expected that he will develop and cultivate the seven factors of enlightenment.” The rest as in §12.