The following verses imply a future or process of sanctification: 2Ti 2:21 If a man therefore purge himself from these, he shall be a vessel unto honour, sanctified, and meet for the master’s use, and prepared unto every good work. So being sanctified is conditional on us purging ourselves. Then in these scriptures we are sanctified by the Word of God, which is clearly an ongoing process: John 17:17 Sanctify them through thy truth: thy word is truth. John 17:19 And for their sakes I sanctify myself, that they also might be sanctified through the truth. Eph 5:26 That he might sanctify and cleanse it with the washing of water by the word, 1Th 5:23 And the very God of peace sanctify you wholly; and I pray God your whole spirit and soul and body be preserved blameless unto the coming of our Lord Jesus Christ. So Paul is praying that we would be wholly sanctified, clearly meaning that sanctification is an ongoing process. For more about this see http://www.biblebb.com/files/ryle/are_we_sanctified.htm and http://bible.org/article/regeneration-justification-and-sanctification.
So we can see that there is an ongoing and conditional sanctification are taught in Scripture. There is also a past sanctification – see https://word.spiritbodysoul.com/sanctification.
Scriptures which we can find that imply a process of becoming holy include the following: Ro 6:19, 2Co 7:1, 1Th 3:13, 4:7, 1 Tim 2:15, Heb 12:14 and 1Pe 1:15. None of these verses state that we are not yet holy already, but they state that we are to yield our members to holiness (Ro 6:19), be holy (1 Pe 1:15-16), follow holiness (Heb 12:14), perfect (mature) holiness (2 Cor 7:1), be established in holiness (1 Thess 3:13), God has called us to holiness (1 Thess 4:7) and about the need to continue in holiness (1 Tim 2:15).
Its interesting that the issue of whether sanctification was accomplished through what Jesus did on the cross and was available to the believer as soon as they believe or was a subsequent experience to salvation (a “second work of grace”) caused a huge split in the Azusa Street Revival. See for example http://www.revival-library.org/pensketches/am_pentecostals/durham.html ‘William Durham… began a preaching mission at the Upper Room Mission in Los Angeles but, despite his brilliant oratory and pulpit presence, the congregation ejected him over sanctification teaching of the “Finished Work.” This teaching repudiated the holiness doctrine of sanctification as a second work of grace and instead declared that everything a believer would ever need was included in the finished work of Christ on the cross. This repudiation of the Holiness doctrine of sanctification as a “second work of grace,” argued that the “finished work” of Christ on Calvary becomes available to the believer at the time of justification. The benefits of Calvary are therefore appropriated for sanctification over the entire period of the Christian’s life, rather than at a single subsequent moment, as was believed by most Pentecostals in Durham’s day. ‘