بُلُوغُ الْمَرَامِ
Bulugh al-Maram 1097
Marriage
وَعَنِ اِبْنِ عَبَّاسٍ رَضِيَ اَللَّهُ عَنْهُمَا; { أَنَّ رَسُولَ اَللَّهِ - صلى الله عليه وسلم -أَمَرَ رَجُلاً أَنْ يَضَعَ يَدَهُ عِنْدَ اَلْخَامِسَةِ عَلَى فِيهِ, وَقَالَ: إِنَّهَا مُوجِبَةٌ } رَوَاهُ أَبُو دَاوُدَ, وَالنَّسَائِيُّ, وَرِجَالُهُ ثِقَات ٌ [1] .
Narrated Ibn Abbas (RA): Allah's Messenger (ﷺ) ordered a man to put his hand on his mouth when he came to the fifth pronouncement and said, "It would be the deciding one." [Reported by Abu Dawud and an-Nasa'i. It's narrators are reliable].
Sunnah.com reference: Book 8, Hadith 154