Induvalu Suresh, 35, hacked off his little finger last month before wrapping it in a rupee note and dropping it in a Hindu temple donation box in the country's south, according to the Times of India.
The owner of a granite business, from Ramanagara near the southern city of Bangalore, said he had vowed to make the unusual gesture of gratitude if the mother-son duo of the famed Gandhi dynasty were given bail.
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"I wrapped the finger in a 1,000 rupee ($15) note with a letter thanking God for granting bail to Sonia and Rahul and dropped it in the hundi (donation pot)," Suresh told the newspaper.
"I did not feel the pain when I cut my finger. Later, I went to the hospital adjacent to the temple and told the doctor that I lost my finger while repairing the AC compressor of my car," he said.
The Gandhis, leaders of the Congress party which was crushed in the 2014 general election, were summoned to court last month over allegations they misused funds of a newspaper once run by the family.
The pair were given bail in the case brought by a politician from the ruling Bharatiya Janata Party (BJP).
The paper was launched by India's first prime minister Jawaharlal Nehru and closed in 2008. Sonia Gandhi, widow of Nehru's grandson Rajiv, later became the chief patron of the trust that ran the publication.
A Congress lawmaker has reportedly thanked Suresh for the finger sacrifice but stressed the party was not keen on "sycophancy of pain".
The Gandhis still have legions of loyal supporters despite their party's drubbing in the polls by the BJP.
The Nehru-Gandhi dynasty has provided three prime ministers and its Congress party has dominated Indian politics since independence.
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