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  

"A man who felt something during Salah complained to the Prophet ﷺ. He said: 'Do not stop praying unless you notice a smell or hear a sound.'"  

شُكِيَ إِلَى النَّبِيِّ ﷺ الرَّجُلُ يَجِدُ الشَّىْءَ فِي الصَّلاَةِ قَالَ لاَ يَنْصَرِفْ حَتَّى يَجِدَ رِيحًا أَوْ يَسْمَعَ صَوْتًا  

He should not cease (to pray) unless he hears a sound or perceives a smell (of passing wind).  

شُكِيَ إِلَى النَّبِيِّ ﷺ الرَّجُلُ يَجِدُ الشَّىْءَ فِي الصَّلاَةِ حَتَّى يُخَيَّلَ إِلَيْهِ فَقَالَ لاَ يَنْفَتِلُ حَتَّى يَسْمَعَ صَوْتًا أَوْ يَجِدَ رِيحًا  

[Machine] "He (the man) complained to the Messenger of Allah ﷺ that during his prayer, he feels that he has passed gas, so he said: It does not nullify the prayer until he finds a smell or hears a sound."  

أَنَّهُ شَكَا إِلَى رَسُولِ اللهِ ﷺ الرَّجُلُ يَجِدُ الشَّيْءَ فِي الصَّلَاةِ يُخَيَّلُ إِلَيْهِ أَنَّهُ قَدْ كَانَ مِنْهُ فَقَالَ لَا يَنْفَتِلُ حَتَّى يَجِدَ رِيحًا أَوْ يَسْمَعَ صَوْتًا  

"A complaint was made to the Prophet about a man who sensed something (some doubt about his ablution) during prayer. He said: 'No (he does not have to perform ablution) unless he notices a smell or hears a sound.'" (Using translation from Ibn Mājah 513)  

شُكِيَ إِلَى النَّبِيِّ ﷺ الرَّجُلُ يَجِدُ الشَّيْءَ فِي الصَّلَاةِ فَقَالَ «لَا يَنْصَرِفْ حَتَّى يَجِدَ رِيحًا أَوْ يُسْمَعَ صَوْتًا»