Sheikh Salman al-Oadah
Weak hadîth, regardless of the degree of weakness cannot be used as evidence for establishing any matter of law. They cannot be relied upon.
However, it is alright to use weak hadîth to support and encourage virtuous acts that are established by other authentic evidence, provided those weak hadîth are neither peculiar in their meaning nor very weak in their chains of transmission.
For example, congregation prayer is an established practice in Islamic Law. Therefore, it is allowed for us to relate a moderately weak hadîth to support the importance of congregational prayer and to encourage people to pray in congregation.
And Allah knows best.
Source: Islam Today