How should a worshipper sit if he is unable to sit muftarishan in prayer?
Question

How should a worshipper sit if he is unable to sit muftarishan in prayer because sitting in this manner is too difficult?
Praise be to Allah.It is recommended (mustahabb) for the worshipper to sit muftarishan in three places in the prayer:
1. Between the two prostrations
2. In the first tashahhud if the prayer has two tashahhuds.
3. In the tashahhud if the prayer has one tashahhud, such as a two-rak‘ah prayer.
What is meant by iftirash (sitting muftarishan) is sitting with the right foot held upright on the toes, whilst sitting on the left foot.
Women are subject to the same ruling as men in this regard, because the words of the Prophet (blessings and peace of Allah be upon him), “Pray as you have seen me praying” (narrated by al-Bukhari, 631) are also addressed to women.
This manner of sitting is one of the sunnahs of prayer, but it is not obligatory. The one who does it will be rewarded for it, but there is no sin on the one who does not do it.
It says in Fatawa al-Lajnah ad-Da’imah (6/446): The Sunnah is to sit muftarishan, sitting on the left foot between the two prostrations, with the right foot held upright, and to do likewise in the first tashahhud. In the second tashahhud, the Sunnah is to sit mutawarrikan (tawarruk), which means slipping the left foot under the right calf, with one’s posterior on the ground. All of this is recommended (mustahabb). If the worshipper sits mutawarrikan in the first tashahhud and sits muftarishan in the second tashahhud, that does not render his prayer invalid. End quote.
If the worshipper is not able to sit muftarishan, because he is heavy, or he feels pain in his feet, or for other reasons, there is nothing wrong with him sitting in whatever manner is easy for him, because Allah, may He be exalted, says (interpretation of the meaning):
{So fear Allah as much as you are able} [at-Taghabun 64:16].
And the Prophet (blessings and peace of Allah be upon him) said: “If I instruct you to do something, then do as much of it as you are able.” Narrated by al-Bukhari (7288) and Muslim (1337).
It says in Asna al-Matalib (1/164): However the worshipper sits at the points in the prayer where sitting is required, it is valid, but the best is to sit mutawarrikan in the final sitting and to sit muftarishan in all other sittings. End quote.
And Allah knows best.