Tawasul is a Quranic concept.
Quran 5:35: Allah swt instructs us to seek intercession.
Quran: Al-Ma'idah 5:35
Translation: Maarif ul-Quran

O those who believe, fear Allah and seek the wasiIlah of nearness to Him, and carry out Jihad in His way so that you may succeed.

یَـٰۤأَیُّهَا ٱلَّذِینَ ءَامَنُوا۟ ٱتَّقُوا۟ ٱللَّهَ وَٱبۡتَغُوۤا۟ إِلَیۡهِ ٱلۡوَسِیلَةَ وَجَـٰهِدُوا۟ فِی سَبِیلِهِۦ لَعَلَّكُمۡ تُفۡلِحُونَ

Reference  : Quran: Al-Ma'idah 5:35
 
Quran 17:57: Even the best of people seek wasila to Allah swt.

Reference: Quran: Al-Isra 17:57

Quran: Al-Isra 17:57
Translation: Dr. Mustafa Khattab, the Clear Quran

˹Even˺ the closest ˹to Allah˺ of those invoked would be seeking a way to their Lord, hoping for His mercy, and fearing His punishment. Indeed, your Lord’s torment is fearsome.

أُو۟لَـٰۤىِٕكَ ٱلَّذِینَ یَدۡعُونَ یَبۡتَغُونَ إِلَىٰ رَبِّهِمُ ٱلۡوَسِیلَةَ أَیُّهُمۡ أَقۡرَبُ وَیَرۡجُونَ رَحۡمَتَهُۥ وَیَخَافُونَ عَذَابَهُۥۤۚ إِنَّ عَذَابَ رَبِّكَ كَانَ مَحۡذُورࣰا

Reference  : Quran: Al-Isra 17:57
 
Quran 12:97-98: Prophet Yusuf's brother's seek intercession of their father with Allah swt.

Reference: Quran: Yusuf 12:97-98

Quran: Yusuf 12:97-98
Translation: Dr. Mustafa Khattab, the Clear Quran

97: They begged, “O our father! Pray for the forgiveness of our sins. We have certainly been sinful.”

 

98: He said, “I will pray to my Lord for your forgiveness. He ˹alone˺ is indeed the All-Forgiving, Most Merciful.”

قَالُوا۟ یَـٰۤأَبَانَا ٱسۡتَغۡفِرۡ لَنَا ذُنُوبَنَاۤ إِنَّا كُنَّا خَـٰطِءِینَ

قَالَ سَوۡفَ أَسۡتَغۡفِرُ لَكُمۡ رَبِّیۤۖ إِنَّهُۥ هُوَ ٱلۡغَفُورُ ٱلرَّحِیمُ

Reference  : Quran: Yusuf 12:97-98
 
Rasulullah intercedes for a blind man.
Jami` at-Tirmidhi 3578
Narrated Uthman bin Hunaif:

A blind man came to the Prophet (ﷺ) and said: “Supplicate to Allah to heal me.” He (ﷺ) said: “If you wish I will supplicate for you, and if you wish, you can be patient, for that is better for you.” He said: “Then supplicate to Him.” He said: “So he ordered him to perform Wudu’ and to make his Wudu’ complete, and to supplicate with this supplication: ‘O Allah, I ask You and turn towards You by Your Prophet Muhammad (ﷺ), the Prophet of Mercy. Indeed, I have turned to my Lord, by means of You, concerning this need of mine, so that it can be resolved, so O Allah so accept his intercession for me (Allāhumma innī as’aluka wa atawajjahu ilaika binabiyyka Muḥammadin nabi-ir-raḥmati, innī tawajjahtu bika ila rabbī fī ḥājatī hādhihī lituqḍā lī, Allāhumma fashaffi`hu fīyya).’”

حَدَّثَنَا مَحْمُودُ بْنُ غَيْلاَنَ، حَدَّثَنَا عُثْمَانُ بْنُ عُمَرَ، حَدَّثَنَا شُعْبَةُ، عَنْ أَبِي جَعْفَرٍ، عَنْ عُمَارَةَ بْنِ خُزَيْمَةَ بْنِ ثَابِتٍ، عَنْ عُثْمَانَ بْنِ حُنَيْفٍ، أَنَّ رَجُلاً، ضَرِيرَ الْبَصَرِ أَتَى النَّبِيَّ صلى الله عليه وسلم فَقَالَ ادْعُ اللَّهَ أَنْ يُعَافِيَنِي ‏.‏ قَالَ ‏"‏ إِنْ شِئْتَ دَعَوْتُ وَإِنْ شِئْتَ صَبَرْتَ فَهُوَ خَيْرٌ لَكَ ‏"‏ ‏.‏ قَالَ فَادْعُهُ ‏.‏ قَالَ فَأَمَرَهُ أَنْ يَتَوَضَّأَ فَيُحْسِنَ وُضُوءَهُ وَيَدْعُوَ بِهَذَا الدُّعَاءِ ‏"‏ اللَّهُمَّ إِنِّي أَسْأَلُكَ وَأَتَوَجَّهُ إِلَيْكَ بِنَبِيِّكَ مُحَمَّدٍ نَبِيِّ الرَّحْمَةِ إِنِّي تَوَجَّهْتُ بِكَ إِلَى رَبِّي فِي حَاجَتِي هَذِهِ لِتُقْضَى لِي اللَّهُمَّ فَشَفِّعْهُ فِيَّ ‏"‏ ‏.‏ قَالَ هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ غَرِيبٌ لاَ نَعْرِفُهُ إِلاَّ مِنْ هَذَا الْوَجْهِ مِنْ حَدِيثِ أَبِي جَعْفَرٍ وَهُوَ غَيْرُ الْخَطْمِيِّ وَعُثْمَانُ بْنُ حُنَيْفٍ هُوَ أَخُو سَهْلِ بْنِ حُنَيْفٍ ‏.‏
Grade: Sahih (Darussalam)
Reference  : Jami` at-Tirmidhi 3578
In-book reference  : Book 48, Hadith 209
 
Tawasul isn't limited to just the Prophets. Umar asks Al-Abbas to pray for rain in times of drought.

Reference: Sahih al-Bukhari 3710

Sahih al-Bukhari 3710
Narrated Anas:

Whenever there was drought, `Umar bin Al-Khattab used to ask Allah for rain through Al-`Abbas bin `Abdul Muttalib, saying, "O Allah! We used to request our Prophet to ask You for rain, and You would give us. Now we request the uncle of our Prophet to ask You for rain, so give us rain." And they would be given rain."

حَدَّثَنَا الْحَسَنُ بْنُ مُحَمَّدٍ، حَدَّثَنَا مُحَمَّدُ بْنُ عَبْدِ اللَّهِ الأَنْصَارِيُّ، حَدَّثَنِي أَبِي عَبْدُ اللَّهِ بْنُ الْمُثَنَّى، عَنْ ثُمَامَةَ بْنِ عَبْدِ اللَّهِ بْنِ أَنَسٍ، عَنْ أَنَسٍ ـ رضى الله عنه أَنَّ عُمَرَ بْنَ الْخَطَّابِ، كَانَ إِذَا قَحَطُوا اسْتَسْقَى بِالْعَبَّاسِ بْنِ عَبْدِ الْمُطَّلِبِ، فَقَالَ اللَّهُمَّ إِنَّا كُنَّا نَتَوَسَّلُ إِلَيْكَ بِنَبِيِّنَا صلى الله عليه وسلم فَتَسْقِينَا، وَإِنَّا نَتَوَسَّلُ إِلَيْكَ بِعَمِّ نَبِيِّنَا فَاسْقِنَا‏.‏ قَالَ فَيُسْقَوْنَ‏.‏
Reference  : Sahih al-Bukhari 3710
In-book reference  : Book 62, Hadith 60
 
If the living can interecede, can the dead intercede for us too?
Quran 3:154: Those who die in the way of Allah are not dead, they are living.
Quran: Ali 'Imran 3:169
Translation: Maarif-ul-Quran

And never take those killed in the way of Allah as dead. Rather, they are alive, with their Lord, well-provided,

وَلَا تَحۡسَبَنَّ ٱلَّذِینَ قُتِلُوا۟ فِی سَبِیلِ ٱللَّهِ أَمۡوَ ٰتَۢاۚ بَلۡ أَحۡیَاۤءٌ عِندَ رَبِّهِمۡ یُرۡزَقُونَ

Reference  : Quran: Ali 'Imran 3:169
Additional References:
 
The Prophet spoke to the dead of Badr, stating that the dead hear better than the living.

Reference: Sahih al-Bukhari 1370

Sahih al-Bukhari 1370
Narrated Ibn `Umar:

The Prophet (ﷺ) looked at the people of the well (the well in which the bodies of the pagans killed in the Battle of Badr were thrown) and said, "Have you found true what your Lord promised you?" Somebody said to him, "You are addressing dead people." He replied, "You do not hear better than they but they cannot reply."

حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا يَعْقُوبُ بْنُ إِبْرَاهِيمَ، حَدَّثَنِي أَبِي، عَنْ صَالِحٍ، حَدَّثَنِي نَافِعٌ، أَنَّ ابْنَ عُمَرَ ـ رضى الله عنهما ـ أَخْبَرَهُ قَالَ اطَّلَعَ النَّبِيُّ صلى الله عليه وسلم عَلَى أَهْلِ الْقَلِيبِ فَقَالَ ‏"‏ وَجَدْتُمْ مَا وَعَدَ رَبُّكُمْ حَقًّا ‏"‏‏.‏ فَقِيلَ لَهُ تَدْعُو أَمْوَاتًا فَقَالَ ‏"‏ مَا أَنْتُمْ بِأَسْمَعَ مِنْهُمْ وَلَكِنْ لاَ يُجِيبُونَ ‏"‏‏.‏

Reference  : Sahih al-Bukhari 1370
In-book reference  : Book 23, Hadith 122