ENOfficial
Narrated Abdullah ibn Umar: Sa'id ibn Ziyad ibn Subayh al-Hanafi said: I prayed by the side of Ibn Umar and I put my hands on my waist. When he finished his prayer, He said: This is a cross in prayer; the Messenger of Allah (ﷺ) used to forbid it.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا هَنَّادُ بْنُ السَّرِيِّ، عَنْ وَكِيعٍ، عَنْ سَعِيدِ بْنِ زِيَادٍ، عَنْ زِيَادِ بْنِ صُبَيْحٍ الْحَنَفِيِّ، قَالَ صَلَّيْتُ إِلَى جَنْبِ ابْنِ عُمَرَ فَوَضَعْتُ يَدَىَّ عَلَى خَاصِرَتَىَّ فَلَمَّا صَلَّى قَالَ هَذَا الصَّلْبُ فِي الصَّلاَةِ وَكَانَ رَسُولُ اللَّهِ صلى الله عليه وسلم يَنْهَى عَنْهُ .
sunnah.com