This Book explains in the light of Quran and Hadis why Islamic festivals cannot be celebrated at the same day all over the world. Islamic calendar depends on the sighting of the moon. Some La-Lazhabi groups trying to force all Muslim to observe Eid and other festivals on the same day. The book exposes their false, fanciful Ideas. This book was published by Khanqa-E-Aminia-Asgaria, Sylhet, Bangladesh in 2012. The Arabic Title of the book is: "Al-Bayanul Jami' Ibrtal Ikhtilafil Matali'" [Discussion On the importance of Moonrise and Sunrise at different time and places.