Q) Mawlid was not practiced or arranged by any of the Sahaba, nor is there any proof of it being done by Tabiyeen, these are the Islaaf whom we follow and choosing their way is the safest path.
Answer: First of all, it is false to say this because Prophet (Peace be upon him) himself celebrated the day of his birth as proven from Sahih Muslim that Prophet (Peace be upon him) was asked about fasting on monday and he replied "He was born on this day and reveletion was sent on him" [See above the heading called "Istadlal from ahadith, Proof # 1], above all, Allah azza Wajjal Himself takes the "DAYS OF PROPHETIC BIRTHS AS DAYS OF PEACE" [See Qur'an 19:15]
Secondly, the Salafis are asked to bring forward a categorical hadith in which Prophet (Peace be upon him) forbade Mawlid, remember to prove something haram you need a more stronger proof whereas even silence goes in favous of us Sunnis due to this following hadith:
عن أَبي الدرداءِ قالَ: قالَ رسولُ الله صلى الله عليه وسلّم: «ما أَحلَّ الله في كتابهِ فهوَ حَلالٌ، وما حَرَّمَ فهوَ حَرامٌ، وما سَكَتَ عنهُ فهوَ عَفْوٌ، فاقْبَلوا مِنَ
الله عافِيَتَهُ، فِانَّ الله لم يَكُنْ ليَنْسَى شَيْئاً، ثمَّ تلا:وَمَا كَانَ رَبُّكَ نَسِيًّا
رواه البزار والطبراني في الكبير، وإِسناده حسن ورجاله موثقون .
Translation: Abu Darda (RA) narrates that the Prophet (salallaho alaihi wasalam) said: Whatever Allaah has permitted in His Book is Halaal, whatever He has forbidden is Haraam, "AND ANYTHING OVER WHICH THERE IS SILENCE IS PARDONED" so accept the pardon of Allaah, for Allaah cannot be forgetful. Then he recited this verse: ‘and your Lord is never forgetful’ [Maryam 19:64].[Imam Haythami in Majma uz Zawaid 1:171, Hadith No. 794]
Imam Haythami (rah) said: It is narrated by Al-Bazzar and Tabarani in his Kabir with "Hassan chain having reliable narrators"
This hadeeth is also classified as Sahih by Nasir ud-din Albani in his Silsilat as Sahihah (5/325)
Hence according to this hadith the Silence proves Mawlid to be allowed because the Asl for this is found in Qur'an and Sunnah as so many proofs have been shown above.
Thirdly even if assuming Sahaba or Tabiyeen did not do it (although no proof of Nafi exists) then there are many things which were not practiced by Sahaba and Tabiyeen, but later Ulama derived rulings on them looking at the principles, Therefore If anything does not contradict the principles of Shariah then it has always been allowed, for example the knowledge of al-Jarh wa't Ta'deel in hadith, the knowledge of Asma ur Rijaal, putting Araab (punctuation) on Qur'an, Building minarets on mosques, narrating hadiths with chain of narrators etc... The point is that their Asl is found in Shariah, similarly the Asl for rejoicing on Mawlid is found in Qur'an itself let alone Sunnah where it is definitely found too.
Q) Mawlid is Bidat al Dhalalah (blameworthy innovation), Prophet (Peace be upon him) said in rigorously authentic ahadith that All bidahs are misguidance and all misguidance are in the fire.
Answer: This hadith is not general but rather specific as classical scholar Imam Ibn Hajr al Haythami (rah) explained:
وفي الحديث "كل بدْعة ضلالة وكل ضلالة في النار" وهو محمول على المحرمة لا غي
Translation: That which is narrated in Hadith that All innovations are evil and all evil are in hell fire, This hadith will be applied for Bidat al Muhrima (i.e. category of haram innovations only) not others.[Al Haytami in Fatawa al Hadithiyyah, Volume No.1 Page No. 109, Published by Dar ul Fikr, Beirut, Lebanon]
Secondly, such terminology is used in Shariah many times, for example Quran states: "Verily you and what you worship apart from Allah are the fuel of hell" (Qur'an 21:98)
We all know that Jesus is worshiped by Christians, now if we make this ayah general then Naudhobillah Jesus shall become fuel of hell fire too (Audhobillah Min Dhalik), therefore we have to understand the reality behind words of Prophet (Peace be upon him), the Bidahs which Prophet forbade were all new innovations which contradicted shariah, the dalil for this could be found in Sahih Bukhari
Volume 3, Book 49, Number 861: (Sahih Bukhari - Muhsin Khan Wahabi translation)
Narrated Aisha: Allah's Apostle said, "If somebody innovates something which is not in harmony with the principles of our religion, that thing is rejected."