Question: Some people in our mosque do sajdah on a wooden block. Why is that?
Answer: These people are probably Shia Muslims. Just like you have Protestants and Catholics in Christianity, in the same way, in islam, we have Sunnis, and that is what we are, and we have Shias. Shias believe in the Quran, and have their own hadiths, which were compiled nearly 2 centuries after the Sunni hadiths were collected.
Their acts of worship are similar, though not the same as ours, and the sajdah-on-a-wooden-block is one such example.
Their broad beliefs are similar to ours, but they differ in the particulars.
Shias portray intense love for sayyiduna Ali (ra), and for the descendants of sayyiduna Ali and his wife sayyidatuna Fatima azzahraa (ra). Their descendants are known as the ahlul bayt, and with respect to this love for ahlulbayt, we are same. We both respect the likes of sayiduna ali, hasan, husayn, zain ul abideen, muhammad al baqir, ja’far assadiq, musa kadhim and other great ulema of ahlulbayt bayt. However, the shias do not like the sahabah (ra), and extremist Shias consider it a reward to curse the Sahabah. This is very regrettable.
The best thing to do is to leave the Shias to do their own thing. As long as they do not interfere with you, leave them be.
Do not go to perform salah in their place of worship, otherwise you’ll have to repeat your salah. Salah behind a Shia imam is not valid.