Since you want proof, here it is. These are just a few examples, you’ll find examples like this in all four schools.
Imam al-Nawawi [al-Shafi'i] (d. 676 AH) recommends seeking intercession through the Prophet ﷺ - and mentions that this is the position of his Shafi'i colleagues in general!
He said in his al-Majmu' (see also HERE) the following:
ثم يرجع إلى موقفه الأول قبالة وجه رسول الله صلى الله عليه وسلم ويتوسل به في حق نفسه ، ويستشفع به إلى ربه سبحانه وتعالى ، ومن أحسن ما يقول ما حكاه الماوردي والقاضي أبو الطيب وسائر أصحابنا عن العتبي مستحسنين له قال : " كنت جالسا عند قبر رسول الله صلى الله عليه وسلم فجاء أعرابي فقال : السلام عليك يا رسول الله سمعت الله يقول ( { ولو أنهم إذ ظلموا أنفسهم جاءوك فاستغفروا الله واستغفر لهم الرسول لوجدوا الله توابا رحيما } ) وقد جئتك مستغفرا من ذنبي مستشفعا بك إلى ربي ثم أنشأ يقول :
يا خير من دفنت بالقاع أعظمه *** فطاب من طيبهن القاع والأكم
نفسي الفداء لقبر أنت ساكنه *** فيه العفاف وفيه الجود والكرم
ثم انصرف فحملتني عيناي فرأيت النبي صلى الله عليه وسلم في النوم فقال : " يا عتبي الحق الأعرابي فبشره بأن الله تعالى قد غفر له
Then he (i.e. the one visiting the grave of the Prophet ﷺ) should return to his original position facing the Messenger of Allah ﷺ -, and he should make him a mean for himself and seek intercession through him unto his Lord subhanahu wa ta'ala.
And the best what can be said [here] is what al-Mawardi (d. 450 AH) and al-Qadhi Abu al-Tayyib (d. 450 AH) and the rest of our [Shafi'i] companions narrated from al-'Utbi and they regarded it as good. He said:
"As I was sitting by the grave of the Prophet, a Beduin Arab came and said: "Peace be upon you, O Messenger of Allah! I have heard Allah saying: "If they had only, when they were unjust to themselves, come unto thee and asked Allah's forgiveness, and the Messenger had asked forgiveness for them, they would have found Allah indeed Oft-returning, Most Merciful" (4:64), so I have come to you asking forgiveness for my sin, seeking your intercession with my Lord." Then he began to recite poetry:
O best of those whose bones are buried in the deep earth,
And from whose fragrance the depth and the height have become sweet,
May I be the ransom for a grave which thou inhabit,
And in which are found purity, bounty and munificence!
Then he left, and I dozed and saw the Prophet in my sleep. He said to me: "O 'Utbi, run after the Beduin and give him glad tidings that Allah has forgiven him.""
- end of quote -
Imam Taqi al-Din al-Subki [al-Shafi'i] (d. 756 AH): The permissibility and goodness of performing Tawassul, Istighatha and Tashaffu' with the best of creation ﷺ
He said in his work Shifa` al-Siqam fi Ziyarat Khayr al-Anam on p. 357 (I had translated the quotes a long time ago, see HERE):
اعلم : أنه يَجُوزُ ، وَيَحسنُ التَّوسلُ ، والاستغاثة ، والتَّشفُع بالنبي صلى الله عليه وسلم إلى ربه سبحانه وتعالى ، وَجوازُ ذلك وَحُسنهُ ؛ من الأمور المعلُومةِ لِكُلِّ ذي دين ، المعروفة من فِعلِ الأنبياء والمرسلين ، وسِيَرِ السلف الصالحين ، والعلماء والعوام من المسلمين ، ولم يُنكِر أَحدٌ ذلك من أهل الأديان ، ولا سُمعَ به في زمن من الأزمان ، حتى جاء ابن تيمية ؛ فَتكلَّم في ذلك بكلام يُلَبِّسُ فيه على الضعفاء الأغمار ، وابتدع ما لم يُسبق إليه في سائر الأعصار ، ولهذا طعن في الحكاية التي تَقدّم ذكرها عن مَالكٍ رحم الله تعالى ، فإنَّ فيها قول مَالكٍ رحم الله تعالى للمنصور : « استشفع به » . ونحن قد بَيّنا صِحّتها ، ولذلك أدخلنا الاستغاثة في هذا الكتاب ، لما تَعرَّضَ إليها مع الزيارة ، وحسبُكَ أنَّ إنكار ابن تيمية للاستغاثة والتوسل قَولٌ لم يقله عالمٌ قبله ، وصار به بين أهل الإسلام مُثْلهٌ
“Know, that it is permissible and good to perform Tawassul, Istighathah (seeking aid) and Tashaffu’ (seeking intercession) through the Prophet ﷺ – unto his Lord subhanahu wa ta’ala. The permissibility and desirability of this is from the matters that are well known among all those who have religion, and well known from the actions of the Prophets and Messengers, and the way of the righteous Salaf, the scholars, and the layman among the Muslims.
No one has denied this from the people of religion, nor has anyone heard about [denying] this in any time until Ibn Taymiyyah came: So he spoke regarding this with words that deceive the weak inexperienced ones and he innovated that which no one from the eras before held.
This is the reason why he attacked the story which has been already mentioned from [Imam] Malik – may Allah have mercy upon him – for it contains the statement of [Imam] Malik to al-Mansur: “Seek intercession through him”. And we’ve already made its health/correctness clear.
And this is why we’ve also mentioned Istighathah in this book, because of the attack against it together with [the attack against] the visiting [of the grave of the Prophet ﷺ and it should be enough for you [to know] that the denunciation of Ibn Taymiyyah against [performing] Istighathah and Tawassul is a statement that no scholar before him had said and he created dissent among the people of Islam by it.”
– end of the quote –
