The Quran

فَمَن لَم يَجِد فَصِيامُ شَهرَينِ مُتَتابِعَينِ مِن قَبلِ أَن يَتَماسّا ۖ فَمَن لَم يَستَطِع فَإِطعامُ سِتّينَ مِسكينًا ۚ ذٰلِكَ لِتُؤمِنوا بِاللَّهِ وَرَسولِهِ ۚ وَتِلكَ حُدودُ اللَّهِ ۗ وَلِلكافِرينَ عَذابٌ أَليمٌ

Muhammad Asad

However, he who does not have the wherewithal shall fast [instead] for two consecutive months¹ before the couple may touch one another again; and he who is unable to do it shall feed sixty needy ones:² this, so that you might prove your faith in God and His Apostle.³ Now these are the bounds set by God; and grievous suffering [in the life to come] awaits all who deny the truth.

I.e., in the manner prescribed for fasting during the month of Ramadan (see 2:183-187). As regards the phrase "he who does not find the wherewithal (lam yajid)", it may indicate either a lack of financial means or the impossibility of finding anyone else who could be redeemed from factual or figurative bondage (see note 5 above). According to many Islamic scholars of our times (e.g., Rashid Ridi', commenting on 4:92), this relates, in the first instance, to circumstances in which "slavery will have been abolished in accordance with the aim of Islam" (Manar V, 337).
Or, alternatively, one needy person for sixty days. The inability to fast for two consecutive months may be due either to ill-health or to really compelling external circumstances (for instance, the necessity of performing labours which require great physical and/or mental vigour and alertness).
Sc., "by showing that you have renounced the practices of the Time of Ignorance" (Razi). In other words, the pronouncement of zihar is not to be considered a divorce, as was the case in pre-Islamic times, but solely as a reprehensible act which must be atoned for by a sacrifice.