(b) The Companion's words "inhasara" (it slipped) or "inkashafa" (it became uncovered) prove that he (peace and blessings be upon him) did not uncover his thigh intentionally. While riding, a person's thigh or awrah may become uncovered because of the wind, a fall or some other reason, so this would not be attributed to (deliberate) uncovering.
(c) In the first narration, the Companion's words "then he moved the waist-wrapper away from his thigh" may possibly mean that the uncovering was due to the narrowness of the lanes through which he (peace and blessings be upon him) was making his mount run. In that case the action would be due to the walls of the lanes, not an act of the Prophet (peace and blessings be upon him); and it would agree with the other narrations transmitted from Isma'il and others, and also with the hadiths in which the thigh is called awrah.
(d) And it is narrated from Sayyiduna Anas (may Allah be pleased with him) that he said: My knee was touching the knee of the Messenger of Allah (peace and blessings be upon him). In it, the uncovering of the thigh is not mentioned.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3239