His father (Ibn 'Umar) said: "One of the sunnahs of the prayer is to hold the right foot upright and point its toes toward the Qiblah, and to sit on the left foot."
Sunan an-Nasa'i Book 12, Hadith 130
← Previous Hadith "One of the sunnahs of the prayer is to spread your left foot beneath you, and hold your right foot upright."

Sunan an-Nasa'i Book 12, Hadith 129 Next Hadith → "I came to the Messenger of Allah (ﷺ) and I saw him raising his hands when he started to pray until they were in level with his shoulders, and when he wanted to bow. When he sat following the first two rak'ahs, he sat on his left foot and held the right foot upright. He placed his right hand on his right thigh and raised his finger for the supplication, and he placed his left hand on his left thigh." He said: "Then I came the following year and I saw them raising their hands inside their Baranis."

Sunan an-Nasa'i Book 12, Hadith 131