Sunan an-Nasa'i, Volume 2, Book 11, Hadith 894 (DarusSalam) ⓘ

It was narrated from Abdullah that: He saw a man praying with his feet together. He said: "He is not following the Sunnah. If he were to shift his weight from one to the other I would like that better."

أَخْبَرَنَا إِسْمَاعِيلُ بْنُ مَسْعُودٍ، قَالَ حَدَّثَنَا خَالِدٌ، عَنْ شُعْبَةَ، قَالَ أَخْبَرَنِي مَيْسَرَةُ بْنُ حَبِيبٍ، قَالَ سَمِعْتُ الْمِنْهَالَ بْنَ عَمْرٍو، يُحَدِّثُ عَنْ أَبِي عُبَيْدَةَ، عَنْ عَبْدِ اللَّهِ، أَنَّهُ رَأَى رَجُلاً يُصَلِّي قَدْ صَفَّ بَيْنَ قَدَمَيْهِ فَقَالَ أَخْطَأَ السُّنَّةَ وَلَوْ رَاوَحَ بَيْنَهُمَا كَانَ أَعْجَبَ إِلَىَّ ‏.‏