Hazrat Shaikh Moulana Muhammad Zakariyya (rahmatullahi ‘alaih) mentioned in Fazaail-e-Aa’maal:
People think that there is no harm if two or four people make a small jamaat and perform salaah at their houses or at their shops. This notion is not correct, due to the fact that firstly, they will be losing the reward of performing their salaah in the masjid, and secondly, they will be losing the reward of performing salaah with a bigger jamaat (i.e. in the masjid). The bigger the congregation who gather to perform the salaah (in the masjid), the more pleasing it is to Allah Ta‘ala.
We should understand that when we are carrying out an action solely to please Allah Ta‘ala, then we should ensure that we do it in the manner most pleasing to Him. It is mentioned in a hadeeth that three things are greatly pleasing to Allah Ta‘ala; a row of musallis performing salaah with jamaat (in the masjid), a person engaged in (Tahajjud) Salaah during the darkness of the night, and a person fighting in the path of Allah Ta‘ala together with the Muslim army.
(Fazaail-e-Aa’maal [Urdu] pg. 342)
Source: Ihyaauddeen.co.za