Moon sighting is Sunnah and not Moon fighting

Narrated Abdullah binUmar:
Allah’s Messenger (ﷺ) mentioned Ramadan and said, “Do not fast unless you see the crescent (of Ramadan), and do not give up fasting till you see the crescent (of Shawwal), but if the sky is overcast (if you cannot see it), then act on estimation (i.e. count Sha’ban as 30 days).
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، عَنْ مَالِكٍ، عَنْ نَافِعٍ، عَنْ عَبْدِ اللَّهِ بْنِ عُمَرَ ـ رضى الله عنهما ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم ذَكَرَ رَمَضَانَ فَقَالَ ‏ “‏ لاَ تَصُومُوا حَتَّى تَرَوُا الْهِلاَلَ، وَلاَ تُفْطِرُوا حَتَّى تَرَوْهُ، فَإِنْ غُمَّ عَلَيْكُمْ فَاقْدُرُوا لَهُ ‏”‏‏.‏
Reference : Sahih al-Bukhari 1906
In-book reference : Book 30, Hadith 16

Abu Huraira reported Allah’s Messenger (ﷺ) as saying:
Observe fast on sighting it (the new moon) and break (fast) on sighting it (the new moon), but if the sky is cloudy for you, then complete the number (of thirty).
حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ سَلاَّمٍ الْجُمَحِيُّ، حَدَّثَنَا الرَّبِيعُ، – يَعْنِي ابْنَ مُسْلِمٍ – عَنْ مُحَمَّدٍ، – وَهُوَ ابْنُ زِيَادٍ – عَنْ أَبِي هُرَيْرَةَ، – رضى الله عنه – أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ ‏ “‏ صُومُوا لِرُؤْيَتِهِ وَأَفْطِرُوا لِرُؤْيَتِهِ فَإِنْ غُمِّيَ عَلَيْكُمْ فَأَكْمِلُوا الْعَدَدَ ‏”‏ ‏.‏
Reference : Sahih Muslim 1081b
In-book reference : Book 13, Hadith 21

`Ammaar ibn Yaasir (may Allah be pleased with him) said: “Whoever fasts the day concerning which there is doubt has disobeyed Abu’l-Qaasim (peace and blessings of Allah be upon him).” (Narrated by al-Tirmidhi, 686; al-Nasaa’i, 2188; classed as saheeh by al-Albaani in Saheeh al-Tirmidhi, 553)