It is from the Sunnah that when a man sits down, he removes his sandals and places them by his side.
حدثنا قتيبة بن سعيد حدثنا صفوان بن عيسى حدثنا عبد الله بن هارون عن زياد بن سعد عن أبي نهيك
من السنة إذا جلس الرجل أن يخلع نعليه فيضعهما بجنبه
No references are available.
[Its isnad is daif] Bukhari narrated it in Adab al-Mufrad, no. 1190, from Qutayba, through the same chain * Abdullah bin Harun is a Hijazi who is majhul (Taqrib), and I have not found anyone who deemed him reliable.