I want to ask does anybody know, How many days did Prophet Yunus / Jonah remained inside the whale until he was carried to the shore "according to the Quran"?
The Quranic story of Yunus37:139-148 is very concise and it does not mention the length of time he spent inside the whale.
From Tafsir Ibn Kathir:
واختلفوا في مقدار ما لبث في بطن الحوت، فقيل ثلاثة أيام، قاله قتادة. وقيل سبعة، قاله جعفر الصادق رضي الله عنه، وقيل أربعين يوماً، قاله أبو مالك. وقال مجاهد عن الشعبي التقمه ضحى، ولفظه عشية، والله تعالى أعلم بمقدار ذلك
They differed as to how long he spent in the belly of the fish. Some said three days; this was the view of Qatadah. Some said seven days; this was the view of Jafar As-Sadiq, may Allah be pleased with him. Some said forty days; this was the view of Abu Malik. Mujahid said, narrating from Ash-Sha`bi, "It swallowed him in the morning and cast him forth in the evening.'' And Allah knows best how long exactly was.
Related to the given answer to the question: How many days did Prophet Yunus / Jonah remained inside the whale?, I want to make a subsidiary point about people who say that it is bida' to recite "la ilaha illa anta subhanaka inni kuntu minaj jwalimeen" 125,000 times, in order to get over a difficulty.
Given the various opinion about how long Prophet Yunus (AS) was in the belly of a whale, it is obvious that he (AS) recited it many times. So, I conclude that reciting it 125,000 times is sensible, and it cannot be bida' simply because that number did not come from the Quran and the Ahadith.