The blessing of reciting Bismillah will make satan as small as a fly......
Imam Ahmad recorded in his Musnad, that a person who was riding behind the Prophet (PBUH) said, "The Prophet's animal tripped, so I said, `Cursed Shaytan.'
The Prophet (PBUH) said,
لَاا تَقُلْ تَعِسَ الشَّيْطَانُ فَإِنَّكَ إِذَا قُلْتَ تَعِسَ الشَّيْطَانُ تَعَاظَمَ وَقَالَ بِقُوَّتِي صَرَعْتُهُ
وَإِذَا قُلْتَ بِاسْمِ اللهِ تَصَاغَرَ حَتى يَصِيرَ مِثْلَ الذُبَابِ
Do not say, 'Cursed Shaytan,' for if you say these words, Satan becomes arrogant and says, 'With my strength I made him fall.'
When you say, 'Bismillah,' Satan will become as small as a fly.
Further, An-Nasa'i recorded in his book Al-Yawm wal-Laylah, and also Ibn Marduwyah in his Tafsir that Usamah bin Umayr said,
"I was riding behind the Prophet (PBUH)..." and he mentioned the rest of the above Hadith.
The Prophet said in this narration,
لَاا تَقُلْ هكَذَا فَإِنَّهُ يَتَعَاظَمُ حَتَّى يَكُونَ كَالْبَيْتِ
وَلكِنْ قُلْ بِسْمِ اللهِ فَإنَّهُ يَصْغَرُ حَتَّى يَكُونَ كَالذُبَابَةِ
Do not say these words, because then Satan becomes larger; as large as a house.
Rather, say, 'Bismillah,' because Satan then becomes as small as a fly.
This is the blessing of reciting Bismillah.
Reference : Sunan Abi Dawud 4982; Book 43, Hadith 210; Book 42, Hadith 4964
The very first ayats of the Qur’ān revealed to Prophet Muĥammad, which begin with: “Read in the name of your Lord...” (Surah 96:1) establish the Islamic etiquette of invoking the name of God at the beginning of every action. This is also in line with the fundamental Islamic principle that God is “the first and the last, the outward and the inward.” (57: 3) He is indeed the real being, the origin and the raison d’être (i.e., purpose for someone or something's existence) of all that exists. In His name, therefore, every movement and action is made, and in His name everything begins.
Bismillah is recommended before performing any Deed
Basmalah (reciting Bismillah) is recommended before starting any action or deed. For instance,
1. Bismillah is recommended before starting a Khutbah (speech).
2. The Bismillah is also recommended before one enters the place where he wants to relieve himself, there is a Hadith concerning this practice.
3. Further, Bismillah is recommended at the beginning of ablution, for Imam Ahmad and the Sunan compilers recorded that Abu Hurayrah, Sa`id bin Zayd and Abu Sa`id narrated from the Prophet (PBUH),لَا وُضُوءَ لِمَنْ لَمْ يَذْكُرِ اسْمَ اللهِ عَلَيْهِ (There is no valid ablution for he who did not mention Allah's Name in it). This Hadith is Hasan (good).
4. Also, the Bismillah is recommended before eating and drinking, for Muslim recorded in his Sahih that the Messenger of Allah said to Umar bin Abi Salamah while he was a child under his care,
قُلْ بِسْمِ اللهِ وَكُلْ بِيَمِينِكَ وَكُلْ مِمَّا يَلِيكَ
- Say Bismillah,
- eat with your right hand and
- eat from whatever is next to you.
Some of the scholars stated that Bismillah before eating is obligatory.
Reference: Riyad as-Salihin 728; Book 2 hadith 1
Ibn 'Abbas (May Allah be pleased with them) reported: The Messenger of Allah (ﷺ) said, "Do not drink in one gulp like a camel, but in two or three (gulps). Mention the Name of Allah (i.e., say Bismillah) when you start drinking and praise Him (i.e., say Al-hamdu lillah) after you have finished (drinking)." [At- Tirmidhi].
وعن ابن عباس رضى الله عنهما قال: قال رسول الله صلى الله عليه وسلم: "لا تشربوا واحداً كشرب البعير، ولكن اشربوا مثنى وثلاث، وسموا إذا أنتم شربتم،واحمدوا إذا أنتم رفعتم".((رواه الترمذي))
Reference: Riyad as-Salihin 758; Book 2, Hadith 31
5. Bismillah before having sexual intercourse is also recommended. The Two Sahihs recorded that Ibn Abbas said that the Messenger of Allah said,
لَوْ أَنَّ أَحَدَكُمْ إِذَا أَرَادَ أَنْ يَأْتِيَ أَهْلَهُ قَالَ
بِسْمِ اللهِ اللَهُمَّ جَنِّبْنَا الشَّيْطَانَ وَجَنِّبِ الشَّيْطَانَ مَا رَزَقْتَنَا
فَإنَّهُ إِنْ يُقَدَّرْ بَيْنَهُمَا وَلَدٌ لَمْ يَضُرَّهُ الشَّيْطَانُ أَبَدًا
If anyone of you before having sexual relations with his wife says,
'In the Name of Allah.
O Allah! Protect us from Satan and also protect what you grant us (meaning the coming offspring) from Satan,'
and if it is destined that they should have a child then, Satan will never be able to harm that child.
Reference : Sahih al-Bukhari 7396; Book 97, Hadith 25; Vol. 9, Book 93, Hadith 493
6. Bismillah before leaving the house
It was narrated from Abu Hurairah that whenever he left his house, the Prophet (ﷺ) would say:
حَدَّثَنَا يَعْقُوبُ بْنُ حُمَيْدِ بْنِ كَاسِبٍ، حَدَّثَنَا حَاتِمُ بْنُ إِسْمَاعِيلَ، عَنْ عَبْدِ اللَّهِ بْنِ حُسَيْنِ بْنِ عَطَاءِ بْنِ يَسَارٍ، عَنْ سُهَيْلِ بْنِ أَبِي صَالِحٍ، عَنْ أَبِيهِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ النَّبِيَّ ـ صلى الله عليه وسلم ـ كَانَ إِذَا خَرَجَ مِنْ بَيْتِهِ قَالَ
" بِسْمِ اللَّهِ لاَ حَوْلَ وَلاَ قُوَّةَ إِلاَّ بِاللَّهِ التُّكْلاَنُ عَلَى اللَّهِ "
“Bismillah, la hawla wa la quwwata illa billah, at-tuklanu ‘ala Allah (In the Name of Allah, there is no power and strength except with Allah, and trust is placed in Allah).”
Reference: Sunan Ibn Majah 3885; Book 34, Hadith 59; Vol. 5, Book 34, Hadith 3885
And so on...
Rest Allah knows best.
Source: Quran, Sunnah, Tafsir Ibn Katheer, In the Shade of the Quran.