Riyad as-Salihin 17:195

Mu'adh bin Anas Al-Juhani (May Allah be pleased with him) said:

The Prophet (ﷺ) forbade (us) from sitting with our legs drawn up to our belly (Ihtiba') during the Friday Khutbah (religious talk before the prayer). [Abu Dawud and At-Tirmidhi] .