He should not return (from prayer) unless he hears a sound or perceives a smell (of passing wind). Abu Bakr and Zuhair b. Harb have pointed out in their narrations that it was 'Abdullah b. Zaid.  

عَنْ عَمِّهِ شُكِيَ إِلَى النَّبِيِّ ﷺ الرَّجُلُ يُخَيَّلُ إِلَيْهِ أَنَّهُ يَجِدُ الشَّىْءَ فِي الصَّلاَةِ قَالَ لاَ يَنْصَرِفُ حَتَّى يَسْمَعَ صَوْتًا أَوْ يَجِدَ رِيحًا قَالَ أَبُو بَكْرٍ وَزُهَيْرُ بْنُ حَرْبٍ فِي رِوَايَتِهِمَا هُوَ عَبْدُ اللَّهِ بْنُ زَيْدٍ  

The Messenger of Allah ﷺ said: If any one of you has pain in his abdomen, but is doubtful whether or not anything has issued from him, be should not leave the mosque unless he hears a sound or perceives a smell.  

قَالَ رَسُولُ اللَّهِ ﷺ إِذَا وَجَدَ أَحَدُكُمْ فِي بَطْنِهِ شَيْئًا فَأَشْكَلَ عَلَيْهِ أَخَرَجَ مِنْهُ شَىْءٌ أَمْ لاَ فَلاَ يَخْرُجَنَّ مِنَ الْمَسْجِدِ حَتَّى يَسْمَعَ صَوْتًا أَوْ يَجِدَ رِيحًا