Answer

Within commonly accepted Jain tradition, there is no widely established or clearly verified account of “another Jain Muni” doing sadhana specifically for 700 years.

Jain scriptures and traditional histories do describe extremely long lifespans and very long periods of tapasya or sadhana, especially in earlier eras of the time cycle, but a specific claim of 700 years of sadhana by a particular Jain muni should only be accepted if it is supported by a recognized Jain text or tradition.

Explanation

In Jain Dharma, beings in earlier time periods had much longer lifespans than people today. Therefore, long periods of spiritual practice are described in Jain cosmology and Tirthankar charitras.

However:

• Exact numbers like 700 years must be treated carefully.
• Not every popular story is scripturally established.
• If the name of the muni or the source text is known, it can be checked more accurately.

Spiritual Understanding

The real focus in Jain Dharma is not merely the number of years of sadhana, but the purity of:

• Samyak Darshan — right faith
• Samyak Jnan — right knowledge
• Samyak Charitra — right conduct
• Tapasya — austerity practiced with detachment

Takeaway

Sorry, I can only provide information that is clearly established within Jain tradition. If you share the name of the muni or the story you heard, I can help check whether it is part of accepted Jain tradition.