Allah himself has permitted and has asked to seek Waseela.
Allah Most High says:
يَا أَيُّهَا الَّذِينَ آمَنُوا اتَّقُوا الله وَابْتَغُوا إِلَيْهِ الْوَسِيلَةَ وَجَاهِدُوا فِي سَبِيلِهِ لَعَلَّكُمْ تُفْلِحُونَ
“O you who believe! Fear Allah and seek a means (waseelah) to him” (Surah al-Ma’ida, V: 35)
Allah Almighty says:
وَمَا أَرْسَلْنَا مِنْ رَسُولٍ إِلَّا لِيُطَاعَ بِإِذْنِ الله وَلَوْ أَنَّهُمْ إِذْ ظَلَمُوا أَنْفُسَهُمْ جَاءُوكَ فَاسْتَغْفَرُوا الله وَاسْتَغْفَرَ لَهُمُ الرَّسُولُ لَوَجَدُوا الله تَوَّابًا رَحِيمًا (64)
"If they had only, when they were unjust to themselves, come to you (Prophet, Sallallahu Alayhi Wasallam) and asked Allah's forgiveness and the Messenger of Allah had asked forgiveness for them, they would have found Allah indeed forgiving and Most Merciful". (Surah al-Nisa, V: 64).
In Surah Al Baqarah, Allah Ta’la says,
لَمَّا جَاءَهُمْ كِتَابٌ مِنْ عِنْدِ الله مُصَدِّقٌ لِمَا مَعَهُمْ وَكَانُوا مِنْ قَبْلُ يَسْتَفْتِحُونَ عَلَى الَّذِينَ كَفَرُوا فَلَمَّا جَاءَهُمْ مَا عَرَفُوا كَفَرُوا بِهِ فَلَعْنَةُ الله عَلَى الْكَافِرِينَ
“And when there came to them a Book from Allah confirming what is with them, although beforehand they had prayed for victory against those without faith…..” (Surah Al Baqarah verse no. 89)
(i) In the commentary of this ayah, it is written in Tafseer-e-Jalalain that they were praying for victory over those who disbelieved saying, “O Allah, help us against them with the Prophet who will be sent at the end of time!”
(ii) According to Tafseer-e-Uthmani, the commentary of this ayah is that ‘Before the revelation of the Quran, the Jews, when vanquished by the infidels, prayed to God: ‘Give us victory and dominance over these infidels by the grace of the Last Prophet and the Book which will be given to Him.’
Someone may object to this by saying that this was an act of the Jews; hence it cannot be used as evidence for Muslims. However, Allah has mentioned this event in the Qur’an and did not condemn this; therefore this demonstrates that if it were impermissible the Holy Qur’an would not have mentioned it.