What is the “difficulty” which makes it permissible to pray sitting down?

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Check below answers in case you are looking for other related questions:
Rulings and issues about praying on a chair
When is it permissible for a person to pray sitting in obligatory prayers?

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Related Answers:
Ruling on the imam walking in the direction of the qiblah to reach the microphone so that the people can hear him
Can he say du ‘aa’ between the two prostrations in words other than those narrated from the Prophet (blessings and peace of Allah be upon him)?
Should she leave the prayer in congregation because her child cries?
Rulings and issues about praying on a chair
When is it permissible for a person to pray sitting in obligatory prayers?

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