Praying behind people who keep their hands to their sides

Some people do not pray behind another Muslim because he leaves his hands by his side stating that it is not part of the prayer. What is the Shari' ruling which enables one who prays with the hands tied to pray behind one who prays with his hands down?

Walaikum assalam wa rahmatullah,

There is scholarly consensus that it is permitted to follow any of the 4 Sunni schools of law. What you mentioned is the position of the Maliki school (may Allah be pleased with them). It is, therefore, valid to follow, and valid to pray behind them without it being disliked for one to do so. [Ibn Abidin, Radd al-Muhtar, 1.564]

As long as the imam fulfills the conditions and integrals of the Hanafi prayer, it is valid to pray behind him. After that, the follower of each madhhab would naturally perform the wajibs and sunnas of their school. [As explained by Mulla Ali al-Qari and Ibn Abidin.] As such, it is virtually impossible for the prayer of any knowledgeable imam to be invalid. (And it is blameworthy to probe.)

Wassalam.
Faraz Rabbani

وَلَوْ سَلَّمَ سَاهِيًا إنْ بَعْدَ إمَامِهِ لَزِمَهُ السَّهْوُ وَإِلَّا لَا

قال ابن عابدين (رحمه الله تعالى) في رد المحتار: (1/564)وَاَلَّذِي يَمِيلُ إلَيْهِ الْقَلْبُ عَدَمُ كَرَاهَةِ الِاقْتِدَاءِ بِالْمُخَالِفِ مَا لَمْ يَكُنْ غَيْرَ مُرَاعٍ فِي الْفَرَائِضِ , لِأَنَّ كَثِيرًا مِنْ الصَّحَابَةِ وَالتَّابِعِينَ كَانُوا أَئِمَّةً مُجْتَهِدِينَ وَهُمْ يُصَلُّونَ خَلْفَ إمَامٍ وَاحِدٍ مَعَ تَبَايُنِ مَذَاهِبِهِمْ ,