Hadith: The people of the pre-Islamic era of ignorance would practice Īlā' (take an oath not to have sexual intercourse with their wives) for a duration of one or two years. Then Allah timed the effective duration of this oath

عن ابن عباس رضي الله عنهما أنه قال: «كان إيلاء أهل الجاهلية السنة والسنتين، ثم وَقَّتَ الله الإيلاء فمن كان إيلاؤُه دون أربعة أشهر فليس بإيلاء».
[قال الهيثمي في مجمع الزوائد: رجاله رجال الصحيح] - [رواه البيهقي وسعيد بن منصور والطبراني]

Ibn ‘Abbās (may Allah be pleased with him) reported: The people of the pre-Islamic era of ignorance would practice Īlā' (take an oath not to have sexual intercourse with their wives) for a duration of one or two years. Then Allah timed the effective duration of this oath. So, for those who swear not to approach their wives for less than four months, the oath is not effective.
[No judgment by Shaykh Al-Albaani is available] - [Al-Bayhaqi - At-Tabaraani - Sa‘eed ibn Mansoor]

Explanation

This tradition of Ibn ‘Abbās (may Allah be pleased with him) indicates that people during the pre-Islamic era of ignorance would swear not to have sexual intercourse with their wives for one or two years. They would also divorce their wives more than three times. So, whenever the waiting period was about to expire, they would restore their wives and then divorce them again. This way, the oath not to have intimacy with the wife, which is known as Īlā', was extremely harmful to women. Therefore, Allah set a duration for an effective oath: four months. Exceeding the four months without intimacy with the wife entails one of two things: divorcing her or resuming intimacy with her. What is less than four months is not considered Īlā'; rather, it is considered a disciplinary measure that a husband uses against the wife. It does not count as an oath of Īlā'.