Reproduced here with thanks from
By Shaykh (Mufti) Muhammad Ibn Adam (HA)
1 It is reported by such a large number of narrators that under normal circumstances it would be impossible for them to conspire a lie.
2 Such a number exists throughout the chain of narration, i.e. from the beginning to the end.
3 The reporters must base their report on sense perception, i.e. on something that is heard or seen.
4 That the narration necessitates certain knowledge for the listener. (Ibn Hajr al-Asqalani, Sharh Nukhba al-Fikr, P.21).