Raising the Hands after the Prayer for Dua.
Scholars have said there aren’t any authentic narrations mentioning the Prophet (ﷺ) raised his hands after the obligatory prayer for Dua. 
- The Prophet (ﷺ) said: Prayer is to be offered in two rak’ahs; and you should recite the tashahhud at the end of those two rak’ahs, and express your distress and humility while raising your hands…
- Abdullah ibn Az-Zubayr (radiAllahu anhuma) said: “The Prophet (ﷺ) never raised his hands until after he completed his prayer.”
- Abu Hurayrah (Radi Allahu anhu) said the Prophet (ﷺ) raised his hands after he made tasleem while facing the Qiblah.
- Isma’il ibn Umayah (radi Allahu Anhu) narrated that whenever the Prophet (ﷺ) completed his prayer he would raise his hands together and say: “My Lord forgive me for my previous and current sins, and my sins committed privately and publicly and forgive me for my immoderate behavior . 
- Anas (radi Allahu anhu) narrated the Prophet (ﷺ) said : “ Any Muslim who raises his hands after the prayer then says:” Oh my God, The God of Ibrahim, Ishaq, and Yaqub, the God of Jibril, Mik’ial, Israfeel, I ask You to answer my supplication because verily I am in need. 
Benefits for this subject:
The above mentioned ahadith were some unauthentic reports which mention the Prophet (ﷺ) raised hands after the obligatory prayers to make dua. Based on some of these narrations and others scholars have stated it’s not from the Sunnah to raise the hands after the obligatory prayers and then make dua. Raising the hands after the obligatory prayers is an innovation.
Shaykh Abdul Aziz bin Baz (رحمه الله) said: “There aren’t any authentic reports that the Prophet (ﷺ) or any of His companions (radi Allahu anhum) used to raise their hands and then supplicate after the obligatory prayer, as far as I am aware. So, based on that to raise the hands after the obligatory prayer is a Bid’ah[ i.e innovation] Nonetheless, there is no harm in making dua after the obligatory prayer without raising the hands. 
Shaykh Muhammad ibn Salih Al-Uthaymeen (رحمه الله) said: “Nothing authentic has been reported that the Prophet (ﷺ) used to raise his hands for dua after the obligatory prayers or sunnah prayers.
Shaykh Muqbil ibn Hadi (رحمه الله) said: “There are no authentic narrations to support the Prophet (ﷺ) raised his hands after the prayer for supplication.”
Some instances in which the Prophet (ﷺ) did raise his hands for Dua:
1: Dua Al-Qunoot
2: Dua for Rain
3: Dua for serenity of the weather and to stop flooding.
Instances when there is no harm to raise the hands after the prayer for Dua:
Scholars consider raising the hands after the prayers an innovation when one takes it as a regular practice and a means to draw closer to Allah at that particular time & place. However if a person does it occasionally, then there is no harm inshallah.
Shaykh Al-Uthaymeen (رحمه الله) No doubt it’s an innovation, and people should avoid raising their hands after the prayer for dua. On the other hand, if a person raised his hands after the obligatory and sunnah prayers from time to time , then there is no harm-inshallah. Reason being, there is a difference between regularly practicing something and occasionally. Actions that are normally practiced must be supported by the Sunnah. 
Shaykh Muqbil (رحمه الله) said: “ There is no harm if a person raises his hands after the prayer sometimes based on the general meaning of the hadith, “Surely Allah is Hayyee, and He loves to conceal the shortcomings of His slaves. If His slave raises his hands, He does not let him go empty handed.”
Conclusion: Overall, scholars consider it an innovation to raise the hands after the obligatory and sunnah prayers if taken as a normal practice. After every prayer a person raises his hands and makes dua’. However, if a person raises his hands sometimes after the prayers and make dua, then there is no harm, and this is the position of Imam Al-Uthaymeen and Imam Muqbil .
Further reading about Bid’ah : https://www.abuaaliyah.com/?cat=6
 There are five conditions for a hadith to be considered authentic: The isnad must be connected.2.A trustworthy narrator must narrate the report from someone similar in his truthfulness. 3. The narrator must be precise in his narration. 4. The hadith must be free from having defects that prevent it from being authentic. 5. The hadith must not be Shath [ A trustworthy narrator contradicts one who is more accurate in his narrations than him ]Expl Al-Bayqooneeyah by Al-Uthaymeen.
 [ Abu Dawud 1296, At-Tirmithi 385, Ibn Majah 1325.] Abdullah ibn Nafi ibn ‘Al-Umay’ah is in the Isnad and he is unknown- refer to Silsilatu Ad-Da’efah 6546
 [ At-Tabarani in Al-Kabeer 13/129] Al-Faydil ibn Sulayman is in the isnad and is Layn- refer to Silsilatu Ad-Da’efah 2544
 [ Al-Uqaylee in Du’afa 3/850]Ali ibn Zayd Jad’an is in the Isnad and he is a weak narrator- refer to Silsilatu Ad-Da’efah 6/58-59
 Ibn Mubarak 2/732. There are two narrators missing in the Isnad- refer to Silsilatu Ad-Da’efah 4997]
 [ Ibn Sunni (Amal al-Yawm Wal-Laylah) # 135] – There are a list of weak narrators in the isnad-refer to Silsilatu Ad-Da’efah # 5701
 [majmu Fatawa vol11/ 167-168 ]
 Fatawa Nur ala Darb # 6322]
 [ Garatu Al-Ashrata 2/73-74]
 [ Fatawa Nur Ala Darb #6321]
 Fatawa Nur Ala Darb # 6321]
 [ Garatu Al-Ashrata 2/73-74]