Four persons were arrested following a complaint by the victim, they said.
The shocking incident took place in Kudkheda village under Piparia tehsil of Hoshangabad district on April 19, police said.
The tribals suspected the widow indulged in black magic. To punish her, they brought a glass of urine and forced her to drink it. They also thrashed her, police added.
Meanwhile, opposition Congress condemned the incident and alleged the BJP government has failed to protect the honour of women in the State.
Leader of Opposition Ajay Singh termed it as "shameful" and said women are finding it difficult to live with dignity under the BJP government.