Sahih Bukhari

Narrated Hudhaifa that he saw a person bowing and prostrating imperfectly. When he finished his Salat, Hudhaifa told him that he had not offered Salat. The subnarrator added, ""I think that Hudhaifa also said:Were you to die you would die on a ""Sunna"" (legal way) other than that of Muhammad (ﷺ)