To Rejoice in the Prophet (s.a.w.) is an Obligation from Allah (s.w.t.)

بِسۡمِ ٱللهِ ٱلرَّحۡمَـٰنِ ٱلرَّحِيمِ

To rejoice and express happiness for the Prophet (s.a.w.) coming to us is an obligation Given by Allah (s.w.t.) through Qur’an, as He Says: 

سُوۡرَةُ یُونس

... بِفَضۡلِ ٱللَّهِ وَبِرَحۡمَتِهِۦ فَبِذَٲلِكَ فَلۡيَفۡرَحُواْ ... (٥٨) 

… “In the Bounty of Allah and in His Mercy ― in that let them rejoice.” …. (Surah Yunus:58) 

Sayyidina ‘Abdullah ibn ‘Abbas (r.a.) said that, “His Mercy”, refers to the Prophet (s.a.w.), as documented in the many exegeses of that verse.  What greater Mercy did Allah (s.w.t.) Give to us than the Prophet (s.a.w.) himself, of whom Allah (s.w.t.) Says: 

سُوۡرَةُ آل عِمرَان

لَقَدۡ مَنَّ ٱللَّهُ عَلَى ٱلۡمُؤۡمِنِينَ إِذۡ بَعَثَ فِيہِمۡ رَسُولاً۬ مِّنۡ أَنفُسِهِمۡ ... (١٦٤) 

Allah did Confer a Great Favour on the believers when He Sent among them a Messenger from among themselves ... (Surah Ali ‘Imran:164) 

سُوۡرَةُ التّوبَة

لَقَدۡ جَآءَڪُمۡ رَسُولٌ۬ مِّنۡ أَنفُسِڪُمۡ عَزِيزٌ عَلَيۡهِ مَا عَنِتُّمۡ حَرِيصٌ عَلَيۡڪُم بِٱلۡمُؤۡمِنِينَ رَءُوفٌ۬ رَّحِيمٌ۬ (١٢٨) 

Now has come unto you a messenger from amongst yourselves: it grieves him that you should perish: ardently anxious is he over you: to the believers is he most kind and merciful. (Surah at-Tawbah:128) 

سُوۡرَةُ الاٴنبیَاء

وَمَآ أَرۡسَلۡنَـٰكَ إِلَّا رَحۡمَةً۬ لِّلۡعَـٰلَمِينَ (١٠٧) 

We Sent you not, but as a Mercy for all creatures. (Surah al-Anbiya’:107) 

Allah (s.w.t.) also Commands us to honour and venerate the Prophet (s.a.w.), and Informs us that He Sent him: 

سُوۡرَةُ الفَتْح

لِّتُؤۡمِنُواْ بِٱللَّهِ وَرَسُولِهِۦ وَتُعَزِّرُوهُ وَتُوَقِّرُوهُ وَتُسَبِّحُوهُ بُڪۡرَةً۬ وَأَصِيلاً (٩) 

In order that you (O men) may believe in Allah and His Messenger, that you may assist and honour Him, and celebrate His praises morning and evening. (Surah al-Fath:9) 

The scholars of tafsir are in two camps concerning this verse.  The first group considers all of the pronouns to refer to the Prophet (s.a.w.).  The second considers the last pronoun with regards to “glorify Him” to refer to Allah (s.w.t.) but the rest to refer to the Prophet (s.a.w.), in such a way that honouring and venerating the Prophet (s.a.w.) naturally leads to and is considered glorification of Allah (s.w.t.), which the wording of this verse implies. 

Allah (s.w.t.) Says: 

سُوۡرَةُ الحَجّ

... وَمَن يُعَظِّمۡ شَعَـٰٓٮِٕرَ ٱللَّهِ فَإِنَّهَا مِن تَقۡوَى ٱلۡقُلُوبِ (٣٢) 

… and whoever holds in honour the Symbols of Allah, such (honour) should come truly from piety of heart. (Surah al-Haj:32) 

There is no doubt that he and the other prophets are among the greatest symbols of Allah (s.w.t.).