‏الصيام : Hadeeth No:2380 Abu Huraira reported Allaah's Messenger (sallAllaahu alayhi wa sallam) as saying: Observe fast on sighting it (the new moon) and break it on sighting it. But if (due to clouds) the actual position of the month is concealed from you, you should then count thirty (days)....

‏الجهاد والسير‏ : Hadeeth No:4382 It has been narrated on the authority of Anas that the Prophet of Allaah (sallAllaahu alayhi wa sallam) wrote to Chosroes (King of Persia), Caesar (Emperor of Rome), Negus (King of Abyssinia) and every (other) despot inviting them to Allaah, the Exalted. And this Negus was not the one for whom the M...