I have not come across any hadith where RasoolUllah, pbuh, himself went out or climbed a hill to sight the crescent. I have not seen even one where he instructed the sahaba to do this. He questioned them if anyone saw the crescent but did not issue specific orders to go out and climb a hill or a high spot to sight the moon. Neither are there ahadith about sahaba going to a hill in a group and gazing at the sky and waiting for the crescent to appear and some of them seeing the crescent and some not (like we do in India and Pakistan) If this was so crucial, why didn't he do it? If anyone knows of such a hadith, please send me the hadith with reference.