The Messenger of Allah ﷺ used to open the prayer, until she mentioned, "He would recite the tashahhud after every two rakahs, spread out his left foot, keep his right foot upright, and forbid sitting in the manner of the devil's posture."
كان رسول الله ﷺ يستفتح الصلاة إلى أن ذكرت: وكان يقول في كل ركعتين التحية، وكان يفرش رجله اليسرى، وينصب رجله اليمنى، وكان ينهى عن عقبة الشيطان.
Muslim narrated it in "The Prayer" (498), in the context of describing the prayer of the Prophet ﷺ, via Husayn al-Muallim, from Budayl bin Maysara, from Abu Jawza, from Ayesha, who mentioned the same.Some scholars have discussed this, saying that Abu Jawza did not meet Ayesha, but the correct view is that he did meet her.Her statement, "In every two rak'ahs there is the tahiyyah," provides an argument for those who consider the first tashahhud obligatory.Abu Yaala narrated it (4356, edited by al-Athari) via Abdul-Salam bin Harb, from Budayl, with the same chain, with the wording, "The Messenger of Allah would not add anything in the two rak'ahs beyond the tashahhud."This provides evidence for those who say that one should not send blessings upon the Prophet ﷺ in the first tashahhud. This is the view of the majority, contrary to Shafii. See for more, "The Chapter on Sending Blessings upon the Prophet ﷺ."Her statement, "He would spread out his left foot and keep his right foot upright," means that in the first tashahhud he would not sit in tawarruk, unlike the second tashahhud, in which he would sit in tawarruk. This reconciles the hadiths.Whoever applies it to the second tashahhud is compelled to reinterpret the hadith of Abu Humayd and others.It is also possible that he sometimes left off the tawarruk to show that it is a sunnah and not obligatory.The meaning of "the squatting of Satan" was mentioned previously in "The Chapter on the Disliked Iqa."