+Asma Bellounis Wa Alaykum Assalam Wa rahmatullah sister, Tahajjud is a special Salah which is performed in the hours of nighttime. Allah rewards us greatly for reading Tahajjud. It is also Sunnah to read Tahajjud. Rasul Allah (SAW) would stand up and read so much Tahajjud that his feet would become swollen. I hope that helps sister. Shukran.