Presumably by 'scripture', you're referring to one of the ancient texts belonging to one of Shruti, Smriti, Itihasa, Purana and not the works of recent Acharyas. If that is the case, the term 'visistadvaita' cannot be found in the scriptures and it is a relatively modern (post-Ramanuja) invention. Ramanuja himself is not known to have used the term in any of his 9 works including the Sribhashya and the Vedartha Sangraha.
The earliest known reference to the term "visistadavaita" occurs in the 17th verse of the Ramanuja Ashtottara Shatanaama Stotra of Vaduga Nambi also known as Andhrapurna.(Ref: See minutes 7-10 of this video where the presenter makes this point. https://www.youtube.com/watch?v=9eKZmluRd2M&t=420s)
Vaduga Nambi was a disciple of Ramanuja, hence a contemporary although it is quite likely he composed the verse sometime after Ramanuja passed away..
The verse goes:
The term was invented in order to comply with the rules of prosody when composing this verse. The technically correct term that describes Ramanuja's philosophy would be "saviśeṣādvaita" or "non duality (advaita) with differences".
The term Visistadvaita ended up becoming more popular although when discussing the theoretical issues in orthodox circles, saviśeṣādvaita is frequently used as well.
Sudarsana Suri is also said to have used this term in the Tatparya Dipika and the Srutaprakasika (although I have not verified it myself) and Vedanta Desika has defined the term in the Nyaya Siddhanjana. (Ref: 'Antiquity of the term Visistadvaita' by Dr. V Varadachari. I have not seen this paper but a number of other works refer to it. Here is one such citation of this work in this context:)