Joining in Congregational Prayer

How to joining in Jama’ah? How to then complete the missed units?

Obligation of Praying in a Congregation

Hanafi – Waajib to pray with congregation
Hambali – Fard
Shafii – Sunnah

Congregation in Masjid is sunnat mu-akkada

Someone who does not pray his fard salaah in masjid when it is near one’s house, his prayer will be defective.

Congregation’s prayer validity contingent on Imaam’s wudu

Imaam not having wudu invalidates entire congregations’s salaah.

It is not necessary to investigate whether the Imaam has done wudu or done properly. Dhunnu bi (a)l mu`mineena khairan.

However if one happens to know somehow that the Imaam does not have wudu. Or has done wudu by wiping over normal / cloth socks then one needs to repeat his salaah. This is because wiping over cloth socks is not considered a valid way of completing wudu according to all the classical madhhahib.

Crossing the Imaam’s line in a congregation

Is it permissible for muqtadi to stand ahead of Imam in congregational prayers?