A unique book on Astronomy in Islam which explains the importance of Lunar System compared to the Solar System of starting a month, also addresses the issue of moon sighting of starting a Islamic month
"Verily, the death from which you flee will surely meet you, then you will be sent back to (Allah), the All-Knower of the unseen and the seen, and He will tell you what you used to do." [Al-Jumu'ah:8]