كتاب الصلاة
2  
The Book of Prayer
Bulugh al-Maram 239
And in the narration of al-Bukhari narrated by 'Aishah (RA) is:
"This is a practice of the Jews."
وَفِي اَلْبُخَارِيِّ : عَنْ عَائِشَةَ ‏- رَضِيَ اَللَّهُ عَنْهَا‏- أَنَّ ذَلِكَ فِعْلُ اَلْيَهُودِ 1
Reference : Bulugh al-Maram 239
In-book reference : Book 2, Hadith 239
English translation : Book 2, Hadith 236
Hadith Text
Reference