Al-Kāfi - Volume 6 > Prayer and Appeal before Allah for a Son
Hadith #6

عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ سَهْلِ بْنِ زِيَادٍ عَنْ يَعْقُوبَ بْنِ يَزِيدَ عَنْ مُحَمَّدِ بْنِ شُعَيْبٍ عَنِ النَّضْرِ بْنِ شُعَيْبٍ عَنْ سَعِيدِ بْنِ يَسَارٍ قَالَ قَالَ رَجُلٌ لِأَبِي عَبْدِ اللَّهِ ( عليه السلام ) لَا يُولَدُ لِي فَقَالَ اسْتَغْفِرْ رَبَّكَ فِي السَّحَرِ مِائَةَ مَرَّةٍ فَإِنْ نَسِيتَهُ فَاقْضِهِ .

6. A number of our people have narrated from Sahl ibn Ziyad from Ya’qub ibn Yazid from Muhammad Shu’ayb from al-Nadr ibn Shu’ayb from Sa’id ibn Yasar who has said the following: “A man once said to abu ‘ Abd Allah, ‘Alayhi al-Salam, ‘We wish to have a child but the birth of a child has not happened for us.’ He (the Imam) instructed him to say, ‘I ask forgiveness from Allah, my Lord and return to Him in repentance’ one hundred times just before it is dawn. If you forget; do its Qada’ (compensatory prayer for it ).’”