This accident on July 17, 1937 was probably the worst railway accident in India until then. Even if it did not have the highest death toll among accidents prior to that, it certainly attracted the most publicity.
This was the derailment of the 18 Up Punjab Express while approaching Bihta station on the Mughal Sarai-Patna section.
The preceding station at that time was Koelwar. Bihta is about 27 km west of Patna and 17 km west of Danapur.
Initial reports mentioned sabotage as a possibility. However, the truth was more complicated than that.
This picture appears in “Indian Broad Gauge Steam Remembered” by LG Marshall (2009). The caption summarizes the findings of the numerous inquiries into the accident.
You can see that the loco is XB 1916 of the EIR (East Indian Railway).
The reports do not clearly mention where the Punjab Express was coming from, except that it was going from Mughal Sarai to Howrah. In the 1935 Bradshaw its route was shown as being from Lahore via Saharanpur and Lucknow.
The “guilty” loco was based at Jhajha shed and was normally used for express trains from there to Mughal Sarai and back.
Another picture from a magazine of that period (Click to enlarge):
The Inspectorate report on the accident is not available on the net. Some other material such as the judicial inquiry report and the more comprehensive Pacific Locomotive Enquiry report were available some time ago, but not now.
You can search on Google, but do not be misled by an article by Ken Staynor which confuses this with another accident which had occurred in the same general area (east of Patna) in 1934. For more on that accident, see this: